Gas and diesel 727s are 2 different animals. Won't even bolt up to your motor. Besides that, you'll kick yourself going from a 5 speed stick to an auto with no o/d. The 727s they put 3. 08 gears in the rear end to make up for the lack of o/d. The 518s and the Getrags got 3. 55s or 4. 10s. If your truck has 4. 10s and you put a 727 in, you'll be topping out in the high 60s on the freeway... foot to the firewall.
Looks like you live about an hour from me. I'm in Muskego. I happen to have a 4wd 518 that still moves the truck, but has some issues. I'm looking for some parts to swap a Getrag into it, and you should have a few of those parts on that truck of yours. I need a bellhousing, clutch, flywheel, and hydraulic setup. If you're interested, we could maybe work out a deal for my 518 with the transfer case, even though you don't need the x-case, it would give you the yoke you need and you'd have a 2wd with a low range. Either way, if you don't want any of the stuff for your getrag, I'd be glad to take it off your hands for you... .