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

A 97 with have an RE unit. Any 5.2 or 5.9 Magnum will have the RE. The later roller LA motors will have the RH unit so 92 or 93 depending if a LA or Magnum is the last year for the RH.

I also found a 93 van but it had a 5.2 Magnum with the RE44

Sorry, late to the game, but figured I would clarify this just in case it helps someone.

The RE did not start with the Magnum motors. All OBD1 Magnums use the RH, so '95 down. The RE did not start until the OBD2 Magnums which are '96+.

The OBD1 motors use a SBEC which controls OD and LU, but nothing else. The OBD2 motors used the JTEC which controls all the gear changes, not just OD and LU.