It really depends if your problem is created by the fenders/body or chassis rails. For the first one if all the wheel alignments are correct I'd leave well alone. The second may be helped with some adjustable chassis braces to pull/push everything back in alignment.
The only shimming is at the lower rear a-arm mountings to correct for wheel alignment (toe and camber) and I've seen Pantera's with an inch or more of spacing on one side. The challenge is the upper a-arm is fixed, so you alter alignment in shimming, but you could purchase some aftermarket adjustable upper a-arms and then between those and the lower shims you should be able to gain a certain amount of adjustment outward and maintain alignment settings.
Whatever you do it has to be done in conjunction with a 4 wheel alignment and for best results combined with corner weighting.