Swapping for an OD 904?
Chrysler made trucks with slants and overdrive transmissions. The A833 OD. Although the truck transmission can be made to work in an A body, it's a bit of work. The shifter needs to be moved by using a custom bracket or the tail shaft has to be swapped on from an A body transmission.
So, to clarify, there WAS an overdrive transmission that came behind a slant six.