They both have a Torqueflite 904 (3-Speed) or a Torqueflite A500 (Overdrive)? If they both have a 904, the Converter will swap. Likewise if both have an A500, the Converter will swap (just not between the 3-Speed and Overdrive, since the converters are different between the 2)

As far as the Flexplate goes, i don't know for sure.