Need a little guidance from the gurus

A '72? Good. Trans Dapt makes a inexpensive swap kit so someone research.
I like the engine torque strap from these guys in addition. http://www.engine-swaps.com
Search the junk yards and classifieds for a truck or van for a Magnum. With the Lowest of mileage of course. My particular engine I used was out of my daughters wrecked Durango with 80K. It still had the cross hatch hairs from the day it was made. So don't be so afraid, just bring a wrench and check.