only the Mitsubishi version of the a500 will work. all the Chrysler/dodge ones have a completely different bell housing. that means you need to get an automatic transmission from a 1988-1996 mighty max or 1989-1996 van. all autos are wide block so you dont need to worry there.

another option is you can convert the truck to a Manuel transmission. you'll need this stuff listed below from a 1990-1996 truck. the transmission can come from a 1984-1989 2.6l g54b or truck from 1990-1996.

brake/clutch pedal bracket
brake
gas pedal
clutch pedal
clutch cable
clutch cable routing plate on the firewall(need to drill this out from the parts truck)
transmission cross member with mounts
flywheel/clutch assembly
engine back plate
engine bay wiring harness from the parts truck
driveshaft
shifter
speed cable
modify the tunnel so the shifter can go threw the floor
modify the transmission tunnel so the gas pedal will go fully to the floor( ball peen hammer works well here, its not as bad as you think.)

i went threw all this before.