4 Speed manual overdrive transmission for A body

Mtrhead said

Yeah the 1975 cast iron version is a lot more premium the main shaft don't ride on the aluminum housing and wear it out

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I think you mean the c/s .
Behind a regular SBM; if you keep good oil in it, they will wear out other parts long before egging out the c/s hole. And if that does happen, then, any automotive-machine shop can bore that hole out for you and press in a bushing. It ain't even that expensive.