The F250 will make a nice truck. I can't help you on the wiring, but I would think that you would need a 4x4 e40d trans instead of one from a 2wd if you want it to be a plug and play process. The tail-shaft will be different on a 4x4 trans vs a 2wd trans.
You should be able to find a good used 205 t-case pretty easily and cheap. Get one from a 77-79 F100, F150, F250, F350 or 78-79 Bronco. Most had the 205, a few, like mine had the 203 t-case.
econoline bumper diagonal bolt up. same mold as the 73-77 truck bumper, but diff mounting points. I always knew they were the same mold, but like I said I never knew they bolted up. The 78-79 bumpers are hard to find here, I've looked for 4 years for an original one better than mine and can't...
I think it's a van bumper as well. 73-77 and 78-79 truck bumpers both mounted straight up and down & will interchange. the 78-79 bumper is more square though, like in the pic above. I've never seen a truck with the diagonal bolt up like that though, just on the vans. I never knew that they would...
Trucks look awesome. BTW, what is the front bumper off of on the '79? I've never seen one mount up like that on the trucks. Could it possibly be from a van of that era? I've always heard they used the same bumper, but mounted a lil different. I never knew they bolted up to the trucks though...