If you have a mustangII rack and pinion on a straight axle ........your in trouble anyway.No way no how no matter what anybody says .............it cant be done safely. Yep i have seen a few done ,but the guys that did it should be taken behind the barn and shot. You cant mount a rack to the frame of the truck with out big bump steer problem.You also cant mount the rack to the axle with out using a flexable or slider steering shaft ,both of which are very dangerous . As far as the other stuff .The rear needs to mounted first (with a bed on it so you know if the wheels sit in the fender wheels correctly,THEY DONT stock) i recommend just tacking or holding it in with the perches and u-bolts NOT welded till you finish the engine swap.After all the weight is in the truck(ie completely built) you just twist the rear to get your pinion angle and weld the perches.It can be done in the truck.Perches DO NOT need to be welded like it was dump truck trailer hitch.Just a few short welds is all thats need or you will warp the housing. If you heat a spot on a rearend housing red the size of a dime it can pull the axle out of alignment up to 1/4 of and inch.(fix em all the time) We even use a jig to weld perches on now.But i am sure you are not going to build or buy a 4-500 dollar jig. I hope you wrote wrong about the rack on a straight axle.???? smile