This all sounds great guys and thanks so much for the information. I do have a PCV valve already on my car, stock I also increased exhaust to 2.25 some time ago with an easy flow muffler. I don't have my speedometer in sync with the 25" tires yet but I drove to Palm Springs this weekend and used just over a quarter tank of gas to get here, 123.73 total miles using around 6 gallons which puts me a 20.62 mpg. I drive easy, kept it at 60 mph which is really 62.1 mph. I think I'll fill up with gas before leaving to see exactly how much fuel I've used for a truly accurate mpg. I've done some research on HEI and am confident that I can do the transition, have any of you heard of Ignitor? This is used to replace the points only in a point using distributor and if you've heard of this can this be used in place of making the whole wiring change? I'm not looking for short cuts but only want to do what I need to do and wonder if this takes the place of the HEI set up. Regarding differential ratio, I feel the car has great pick up in any gear, which ratio do you recommend with my 225 /6, 76' A833 OD, and 25" tires ?
I just passed up bidding on a 8.75 diff and a set of axles with small bolt pattern on Ebay although I'm not a racer so the 7.25 will suit me until I get the itch to make the change.
Once again all this advice sure beats going into the dark with anything having to do with modifications on our old / sixes. I spend hours reading messages to get general information all the time.
Brian

I really think you can/could/should be getting several more miles per gallon on the highway, and assuming the engine's in good tune, I'm going back to my suggestion that your overall gearing is too tall.
Yes, the Pertronix Ignitor is a legitimate upgrade with a generally good reputation, see this thread, and it is easier to install than HEI, but HEI is a stronger ignition system, and if you are trying for maximum fuel economy, you really want to install the best ignition system you possibly can, within reason. And since you'll want to buy (or configure) a carefully-curved distributor anyhow, and your '63 item likely has some wear on it, I'm not sure keeping the existing distributor is necessarily a good reason to pick the Ignitor vs. HEI. Take a look at this post and this one; those distributors are still out there brand new — here's one, for example.
Then perhaps you might have miscalculated your rear axle ratio, because one does not get anything remotely like great pickup in any gear with 2.9x or 2.7x behind a manual trans with a 1bbl slant-6 engine. Is this the car's original rear axle, do you know? If so, what engine and transmission did the car originally come with? It's best to count quarter-turns of the driveshaft (e.g. by counting the number of rear U-joint caps that face the pavement) as you turn the one lifted rear tire through two revolutions. Then divide the number of quarter-turns by four. Counting whole driveshaft turns makes it much harder to figure out the ratio correctly, because the fractional turn at the end is a guesstimate/judgement call.
How much stop-and-go driving do you do? How much highway driving? When you're on the highway, how fast do you generally cruise?

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

2.76 not peppy... 2.94 in one of the 60's bodied cars (lighter) is not a bad compromise, it's pretty peppy due to the 3.09 1st gear ratio (Beater Valiant has 2.93's and that ratio and with the 1 barrel Holley it was 'fun'... and a definate improvement over the A-904 it had...)... the only thing that's not good is the .73 * 2.94 Overdrive gear ratio, that tends to 'lug' on the highway more than keeping in the engine's sweet spot...

-D.idiot

I'll take your word for it at sea level; I was going off my recollections from "mile high" Denver, where the altitude takes a large chunk out of engine output.

But still, there's only ~10% difference between 2.93 and 2.76...

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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 beg to differ about the 2.76 8 3/4 posi not being peppy. Maybe a stock slant is a slug, which mine was originally, but after the motor rebuild for torque, advancing the cam and distributor recurve, it changed all that.
It is a monster in comparison and that is with a one barrel!

I can hardly wait to install the Super Six set up.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG