should I change gears or tranny???

Labor would be free courtesy of me, I've done O.D. tranny swaps before but on brand X vehicles only, never done a Mopar. Didn't 518's come in Vans or am I tripping??? If I can't find one I guess I'd better follow up on pettybluedarts lead. I did a Dana 60 gear swap about 15 to 20 years ago and from what I do remember it was a friggin' nightmare!!! but I gotta do something...