I'm looking at a 1989 Ford f-250, 2WD single cab, dually rear axle for the 460 motor and the ZF-S42 5-sp tranny. How hard is it to convert the tranny to 4WD? It also has another spare ZF, but it's also 2WD, without the parking brake. Also, not sure on ID for the rear axle, code is 72. I think that's 4.63 gears, but not sure if it's a Sterling 10.25" or dana 80. Any hope for this axle for a wheeling rig? JSM84