What are the most likely Donor vehicles for the A 500 4 speed automatic?

Maybe so. It looked like it was all factory and all the wiring was connected.

Interesting. Did you notice what PCM it had? One big plug or 3 smaller ones? PCM would have been black or silver, black for SBEC or silver for JTEC.

Maybe it had a GC TCM wired into it. No idea that there was a TCM for an RE until just now.