I’ll have to investigate it closer but I have a truck 4-speed overdrive transmission that I’ll be rebuilding but I’ll be using a cast iron main case with a 307 bearing and retainer so that I can bolt it into my 64. Again I’m not 100% sure that it’s possible to change the case and bearing but time will tell.
I have the 4-speed O.D. trans in my RR. Aluminum case. Not sure what it was in originally, (truck - motorhome)
Bolted up directly to my original bellhousing (2892262) . The only thing I did was have a machine shop Bush the front of the case for the countershaft. I understand, because of the aluminum case, the weak point was the case would hog out over time were the countershaft was.
Also, I almost forgot, I had to change the rear trans mount to a later year part. Don't remember the part# but got it from Brewers. They knew which one it was. Bolted right in.
I put about 8,000 miles on mine so far with no issues.
383/438 engine at a dyno of 530 HP.
However, I don't power shift or beat it up.
I don't race it. (do "get on it" though)
Down side...VERY low 1st gear so a significant drop in RPM from 1st to 2nd. For the benefit it's livable.
Great on the highway 75MPH @ 2100 RPM with 3:23 suregrip