The life of a Magnum (and 46RE question)

1998 Durango 4X4, 5.2L with 290K, few water pumps, but valve covers never been off. Trans (42RE?) was done @179K and again @ 213K.
4x4 5.2 would be 44RE. I've seen a few original motor Jeeps with over 370k.

I'd start with vans. Not sure they ever had a 4WD option when the Magnum motors and OD trans were in production. I see them show up at Pull and Save once in a while, I could pull one for you the next I am there with nothing to do. ;-)
Dodge never offered 4x4 vans- Ford did because they got wise that Pathfinder & similar companies were buying Ford spec Danas to put under every kind of van. Vans are a pretty good donor since many vans even had 3spd hydraulic transmissions which means you can use basically whatever transmission you choose. The van 32RHs (904/998), 42s and 44s all have low 1/2 gearsets and I think the better front pump setup than earlier 904s despite being lockup.