You are in luck...it appears you want to do this fairly cheap....I have a Dana 44HD 8 Lug 3.55 geared axle that came out of my 1990 E350 Quigley van. It is complete with brakes/rotors and 4 link system. This is a direct very easy bolt on to your vehcle. The only thing you would have to do is fabricate 2 rear brackets that the 4 link attaches to. (easy and I can provide pictures and dimensions of those brackets0. You would also want to replace the rubber bushings and go with polyurethene (8).
I was thinking around $750.00 Don't see how you could do it cheaper than this!