all of the above, especially the comment by SC of finding a competent shop. i have never had one of these apart, but if they are similar to an early iron, two piece torqueflite, they should be a somewhat simple transmission to rebuild. compared to a modern computer controlled version at least. the concern for a shop is a valid one because some of the internal parts machined appearances may be substantially different than those used today, thus a shop may deem certain parts unusable although they may be fine, plus some may look good, but not be suitable for re-use. this being the equipment and techniques used in the early days left a lot to be desired compared to the cnc machining used exclusively today. also, if no FSM or rebuilding guides for this transmission are available to the shop of your choice, critical clearance dimensions and adjustment procedures may not be used causing your rebuild to have problems maybe from the start. one thing i do know,those things are not the easiest to rassle into place. one other item to think about is the condition of your torque converter. hopefully, all it needs is a good flushing using the appropriate converter flushing machine. if there are problems inside it, i can't begin to tell you where to look for a replacement. what are the symptoms ? whatever you decide, good luck and i hope all turns out well.
if a 55 powerflite transmission for a plymouth is the same except for the bellhousing attaching it to the hemi, i can copy and send you the transmission section from a FSM. i may even have one for a desoto of that vintage to compare info. i'm pretty sure i don't have a 54 chrysler FSM though, but i'll look through my library.
