Alu OD 833

66fs said

Earlier the better. 75 "A" body or "F" body should be good, shifter and all. If you are lucky, it is possible to get one with the smaller 307 front bearing. Then all you have to do is swap the front bearing retainer. The aluminum main housing has a floating countershaft, read sloppy, that can loosen up even more with usage. Try it and find out how she runs. Dump the ATF and put in 90 wt gear oil. I skip to a 64 or 65 cast housing and a new 64-65 countershaft to get everything tight again. Good luck.

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I dunno about that. The 308 bearings came about for a reason, they went to the larger bearing to help make up for the 3-4 gear reversal changing how the power was routed in overdrive (3rd gear on the cluster).

You can buy a 4.8" diameter bearing retainer for the 308 bearing cases (or turn the 5.125" retainer down to 4.8"), and then you can have the 4.3" bellhousing machined out to match the 4.8" retainer. They sell the 4.8" retainers with the bolt pattern for the 308 bearings now, makes putting one behind a big block easier. More info on that on the bottom of this page, they turned it down but I've just bought the 4.8" bearing retainer with the larger bolt pattern since then

Mopar Big-Block A-Body 4-Speed Conversion