It's easy to mate a '68-up engine to a '67-down transmission, but harder to go the other direction. There is no appropriate lockup converter for this what you want to do. Non-lockup custom converters to do this job have been specially built, but I'm not even sure if a custom lockup converter can be made to fit the pre-'68 small-counterbore crank. It may be easiest just to machine the counterbore on the early crank so that it is 1/4" larger (I.D.) and go ahead and use an off-the-shelf lockup torque converter.

I take it you're going with a late-model trans to get the wide-ratio gearset? I did that...once. Didn't like it, not gonna do it again.

My setup involved the installation of an input shaft and some front pump parts from a '66-'67 trans into a '68-'77 non-lockup trans equipped with the '80+ wide-ratio gears. I didn't like the wide-ratio gears. I can understand wanting lockup — it can save you 5% or so on fuel — but just think through how you're going to go about it beforehand, and do the math to figure out your payback period on that and the (very costly) GV unit.

Not too long back I think Charrlie S had posted that because of how the lockup is set up you can only get the lockup torque convertor in the large hub/snout... so you will be in for a late crank, turning the crank pocket on the 66 crank, or a crank kit for a 1968-1975 225...

-D.Idiot

It will not work, with a lock up converter. The pilot on the converter is hollow, to accomadate internal components. With the lock up converter the hole in the pilot is larger, and there is not enough wall thickness to reduce the outside diameter. The same situation holds true with a late 727 trans, the converter cannot get the smaller pilot.

The answer to your question hinges on whether a small-nose, lockup torque converter can be built, or if you can machine the counterbore in your crankshaft, or swap in a '68-'76 crank. If the answer to any of these is "yes", then installing a lockup trans will be simple, though cost may vary depending on parts availability.

The 4-speed autos aren't as sturdy as the 3-speed units, but a properly-built one ought to hold up OK behind a slant-6. Floor, crossmember, and driveshaft mods will be needed. The (discontinued) AREngineering adaptor plate could be used to mount one of these to the slant, but you will still run into the very same torque converter/crank fitment problem.

It seems to me you could probably do a 5-speed manual swap for less than a GV over/underdrive...

Charrlie back in March 10, 2006... when another member had the same problem and I didn't have access to a lockup rebuild book...
here


You 'da man!

-D.idiot

Now, here's another question: is there any difference in strength between early and late model crank shafts? I'm wondering if it would be better for me to get a late model crank, have it balanced and use that instead. Then while everytihng's apart I could balance the whole bottom end...

That is certainly an option, perhaps the best option. I'm pretty sure the cranks are interchangable other than the tranny hookup as long as you don't try to use the cast crank from the late engines.