Help ..904 has died 4 times !

I'll bet the throttle position arm was not adjusted properly = low line pressure in high gear = no fluid to cool = welded plates/clutches.

Aamco is bleeding you IMHO.

1968 and up, all the 904 transmission/converter combos are the same, sans the internal/external balance deal. You have the balance deal covered with your flexplate.

Find someone that races 904's, local drag racers, etc. and see who build their stuff. These are simple transmissions to rebuild. If you can build an engine, you can do a 904 or 727.