I think I am having problems with my BBD on a 1964 225.
(1) I seem to have internal leakage that floods the carb after shut off so that it is hard to start (flooding). I can smell gas. I am sure the float level is correct. The fuel inlet valve looks to be in good condition. The car runs great on the hwy. This is not due to boiling of gas in the carb.

(2) It does have an intermittent problem at idle but only when the auto trans is engaged and I am sitting on the brakes stopped. It will try to cut off then clear itself and idle then maybe do it again. These problems may not be related but then again they may be. Just sitting in neutral idling it runs perfect, not a miss.

For problem #1 I pulled the top off the carb and filled the float bowl and looked for leaks. It was leaking around the gaskets on the venturi cluster assembly. The tips of the venturi tubes where wet but not dripping gas. I found no other leaks. I think the fuel inlet valve is working properly. I put new gaskets on the venturi cluster assembly and this seemed to help but did not solve the problem. Should I try to lower the float level below factory specs to see if this helps? Should I change the fuel inlet valve even though it looks alright? I think I am losing pressure on the fuel line after cut off. Is there any other place the carb can be leaking internally?

I cannot figure out what is causing problem #2. Maybe I have the car idled to low (650 rpm), if i give it a bit of gas sitting on the brake the shake goes away. Could this be a transmission problem? Linkage adjustment or trans adustments? New filter and fluid?

For reference, here is the Carter BBD operation and repair manual (pdf) .

Since you've put new venturi cluster gaskets in already, do the fuel line mod and see if that will alleviate your flooding-on-shutdown problem.
The thing to do here is figure out if it's gagging (going rich) or gasping (going lean). With the engine hot, put the car in Drive and firmly set the handbrake. Go round the back of the car and watch the tailpipe. When the car does its behaviour, check for black exhaust smoke. If it's present, the carb's going rich and the problem is likely related to the hot-restart issue. If not, further diagnosis will be required.
The hot-restart problems suggest the opposite: that fuel pressure is going too high in the line after engine shutoff.
650 is an appropriate engine idle speed in Neutral, but also measure the speed in Drive; sometimes, particularly if the distributor vacuum advance isn't set up right, you can get a very large RPM drop between Neutral and Drive, and that can make problems. Also use a voltmeter to check your line voltage (across the battery) with the engine hot and idling in Drive. If the charging system is slacking off too much at idle, ignition primary voltage can drop enough to affect spark quality negatively. Speaking of which...what is the status of the rest of the engine's tune-up parts and adjustments? What is your baseline ignition timing, which ignition system are you running, and what spark plugs?
No.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks SlantSixDan.

The car has all new Accel wires, pertronix unit in unknown distributor (not the original dizzy), new blue streak distributor cap, new rotor, and with NGK spark plugs recommended here for the peanut head (not the original head). Timing set at about 10 degrees BTDC. I've installed the higher amp alternator with the electronic voltage regulator.

I am suspicious that the distributor and/or the vacuum advance are not right for this set-up. I did hot have the problem of uneven idle in drive with the old distributor.

I could still have wiring problems, I've already done the grounding as recommended here by you and others. I will check the voltage across the battery.

It did not occur to me that I could be getting too much pressure in the fuel line. The fuel line mod that you recommend is already on my list of things to do, I am going to go ahead and get that done.

I will post the distributor id numbers here in the hope that you or others will help me identify it and see if it is right for this sep-up.

The dist number will be interesting, but more practical will be some checks on the function of the dist itself. Put a timing light on the engine at idle (in Neutral and in Drive) and see if the timing mark bounces around rather than remaining steady. Check to make sure the distributor's vacuum advance holds vacuum (can't suck air through the vacuum advance hose), and see that it's connected to the correct nipple on the carburetor. Pop off the distributor cap, grasp the rotor, turn it clockwise and see that it springs back to its original position. Also check your PCV valve to make sure it's the correct one and in good condition, and properly connected.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Actually the timing mark does jump around a bit. I have accelarated the engine with the timing light on and it does advance the timing. The rotor does spring back. The distributor vacuum hose is hooked up properly.I am pretty sure I have the correct PCV valve.

What does a bouncing timing mark indicate?

That'll definitely affect engine idle quality and stability. Could mean a broken or loosened spring in the distributor's mechanical advance mechanism, a loose or failing distributor drive pinion, a slack timing chain, or an incorrectly-connected vacuum advance. You can get visually-obvious advance on rev and rotor springback and still have a mech advance problem if only one of the two springs is faulty. Did you vacuum-check the vacuum advance?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

When I installed the pertronix in the distributor I cleaned and checked it thoroughly. I will do more checking however. The pinion gear looked good, no broke springs, the shaft was tighter than the original dizzy. However something could have changed since I installed it.

I will vacuum check the advance.

I noticed that he dizzy I used had brass fittings unlike the original 64 dizzy. It looked like a better quality distributor.

I have access to distributors for s6 valiants 1960-1965. Which of these models where the best quality and/or which would work better with my application?

Brass fittings...? Where?

The '60-'65 distributors differ primarily in advance curves, not in construction details.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I probably used the wrong terminology, fittings is not exactly correct. However the dizzy did have some brass parts. I have quite a few slant six parts laying around and I liked the look and feel of this particular one, so I used it. It was the only one with brass parts. I will have to look back at it to refresh my memory of what parts were brass. I have no idea what car it came from. I tore my files apart this morn looking for the dizzy # and could not find it. I will be pulling the distributor and taking a closer look at it and will post info here.

Obviously, it is time for me to study and learn and get a better handle on advance curves, springs, etc. I knew this was coming and this idle issue will push me to figure it all out. One of the things I love about the old sl6 are all the mods that can be done and the seemingly endless possibilities to fine tune this engine.

Of the 60-65 distributors are there any that would have a close to ideal advance curve for the set-up that I have?

I checked the RPM at idle in drive as suggested by SlantSixDan and have discovered that I have a large drop in RPM. I believe I may have a problem with the vacuum advance not being set up right as suggested.

I put a timing light on while the car was idling in drive and discovered that I was getting no fire to the #1 spark plug on an itermittent basis. When the timing light failed to light up coincided with the idle problem. I think this means I am getting a weak spark across all the cylinders because of low RPM and the coil not getting enough power. I suppose this could also be a problem with my charging system.

To check this out I re-installed my old points distributor. After a little tuning I had the car running great and the idle problem is much less noticeable and possibly gone.

I want my pertronix back!! Even though I am having idle problems with it, I can tell a difference at speed on the hwy. The pertronix is an improvement.

Since I know little about vacuum advance I am going to try another distributor with the pertronix and see it anything changes.