With the automatic-equipped truck as a donor vehicle, you shouldn't have much trouble. You'll need to swap such things as the radiator, rear crossmember, steering column, and a little wiring, since the TH 400 has an electrically-triggered 3/2 downshift. The front driveshaft spline will be different. As long as both trucks have the same wheelbase, the driveshaft for the auto should swap without a problem. If the wheelbase is different, you'll probably have to have it shortened or lengthened by a driveline shop.
Jerry
