put a a518 its a 727 with overdrive you find it from a ramcharger etc and the electronics its just a cable to a button to turn on off the od , i think it requires to modify the floor tho
http://www.moparts.org/Tech/Archive/auto/28.html
i believe there is some issues with some of the shafts needing oil holes drilled in them. when i spoke with my trans guy about a 518, he suggested getting a gas and a diesel case, apparently the diesel unit has got some better parts in it. valve body choice is somewhat limited for the 518, at least this is what Chris Andrews told me a while back. the electronics adds $$ to it, some controllers are in the $1200-1400 area. i was planning on using a gm4l80e in my car, don't really care about the cutting. but problems are that is an expensive trans, needs a 500-600 bellhousing adapter, the electronic speedometer on the trans would need another $$ adapter to work with my cars speedo, it is about 100 pounds heavier than a 727..