What modern tranny (overdrive) can be mated to a '49-'52 Str 8 ?

[BuickNut]

My Dads '52 Buick Super 4 door has the dynaslush going down and in need of a rebuild. Given that he drives is fairly often, at highway speeds, and in town stop and go, I was wondering what overdrive we could put in there, and what mods would have to be made to the rest of the drive train...(replace torque tube, change rear end ?). I guess I just don't trust the old dynaflow that much to just go ahead and rebuild it... the car has less than 45k miles on it, and is just a nice driver, and he does drive it regular whether permitting with no snow, in the Ohio winters.........any suggestions ? (.....just drrrrriven that Buick as it was meant to ! <img src="http://www.aaca.org/ubbthreads/images/graemlins/laugh.gif" alt="" /> )