Quick advice while I research. Magnum Swap
I would recommend using the magnum, the 96 is a great year to use because it is obd II but doesn't have ccd buss so you can run tach, oil, MIL and temp gauges in dart. The 4x4 trans is easily converted to 2wd by swapping the tail housing. The magnum flex plate will need one hole slightly elongated to bolt right up. If you decide to use a V8 904 and not cut the tunnel, then its pretty much bolt in deal. You can always run a manual pcm from a 5.2 and then wont need a pcm flash. You can leave the auto trans stuff in the wire harness so you can always do the trans at a later date if you want to. Just geting it up and running quickly will be good motivation to go with overdrive.
we are currently doing a 64 in the shop, look under magnum swap thread as well as drive train to follow along. we plan on using the push button if at all possible otherwise we have a pair of buckets and floor shifter out of 65 we can use.
I have a 67 GT convert waiting its turn for a complete magnum swap, od auto and resto but was thinking of swapping a stock 5.2 magnum into it just for fun/demo first as it is a good driver except for noisy rod in brand new 318 la somebody built incorrectly. It has a 904 so it would be literally a bolt in deal, build a harness and install the tanks inc tank and drive it while it waits in line. I want to demo just how easy it is to do this.
The truck is a great deal, pick it up, get the parts to start and go for it. If you need any help, call the shop 541-955-0363. We have all the stuff to do it and will give you lots of advise. Evan magnummopar.com