What are the most likely Donor vehicles for the A 500 4 speed automatic?
Jackpot! I think.
Further reading of Gary's documentation shows that the 42RE was actually introduced in '93 for the GC 4.0 inline six and came with a stand alone TCM.
While I'm not suggesting someone try and use the transmission, it does mean there is a controller for an RE transmission. Probably still needs TPS.
And it would be JY prices.