I have both a 1997 and 1998 minivans. I believe the engine sizes are the same. would the transmissions be interchangable? One has quit, and the other needs transmission work

 

You didn't mention which one is good and which is bad. Yes you can interchange them. But not with out some work. The flexplate needs to stay with the torque converter that is currently attached to it. Also the range sensor (and connector) is different. They use the same pin functions but you need to splice one or the other to stay with its respective sensor. 98 range sensor needs the 98 connector and vise versa. Also the crank sensor may be different. You will need to swap crank sensors to match the connector on the van you will be using.

This explanation woulda been easier had I know which van had the bum trans. You may need a pinout diagram for each TRS to correctly swap connectors. You can buy a splice kit from dodge
Good luck