Help converting my 64 to 66 23 Spline 8A33 to an overdrive ?

do you have a slip style yoke or is it B&T?

that's number one.

after that, i *guess* it can be done? the OD took a different main shaft which in turn took a different tail shaft, but maybe a slip style would work?

a LOT less work and expense would probably be to source a compete OD box.

@AJ/FormS will know for sure what the compatibility is.