Scottie, I didn't have a dif to start with so the cost included buying my 12 bolt. I had it shortened, rebuilt the posi unit, installed 3:73 gears, bought Moser axles, and installed '79 TA disc brakes. This costed $1500 (not cheap!)The suspension is the Jeg's S/S bars (street/strip suspension), panhard bar, and coilovers. That cost around $500. The narrowed frame, and tubs I did my self, materials cost, $20 maybe.
You could probably find someone local to shorten the housing, but I would buy some custom axles from Moser or someone. You can shorten the stock axles, but they won't be very strong. Also on a Ford 8.8, it uses C clips to hold the axles in. You maybe alright since the Z dosn't wieght that much, but if you want more strength, use C clip eliminator kit.