If using a Ford rear with a different pinion relationship to center of vehicle, then that rear end should be modified to compensate to match the offset that Chrysler designed. But for the 8&3/4 you say you're using now, you should be in good shape. Just hold to that 43" center to center measurement for the spring pads and keep them equal distance from the ends of the axle tubes (unless you'd like to fudge it slightly to compensate for tire centering in your wheel wells). Of course this is assuming that you have not used a spring relocation kit. Get your pinion angle set and you're good to go.
