Offset shackles
A-body springs are parallel to the frame rails, no taper front to rear. And the DoctorDiff offset kit for A-bodies is a 1/2" offset front and rear, the springs stay parallel.
The Mopar Performance offset kit has a 1/2" offset on the front hangers and a 3/4" offset on the rear shackles, and is advertised as a 3/4" offset. If you put the spring perches at a 3/4" offset, you put a bind on the front half of the spring (and you still don't get a full 3/4" of tire clearance). If you put the perches at a 1/2" offset, you put a bind on the rear half of the spring. The only way to not put a bind on the spring would be to set the hangers and shackle mounts at an angle to match the offset, so the springs would be angled and everything would be inline (eye bolts and shackles would be parallel to the springs, but the springs wouldn't be parallel to the frame). But that would set up an angle opposite of what you usually want, if the rear springs are splayed it's done so the fronts are narrower than the rears. E-bodies have splayed springs, the front is narrower than the rear. Like anything with suspension there are pros and cons to doing that way.
A-body springs are parallel to the frame rails, no taper front to rear. And the DoctorDiff offset kit for A-bodies is a 1/2" offset front and rear, the springs stay parallel.
The Mopar Performance offset kit has a 1/2" offset on the front hangers and a 3/4" offset on the rear shackles, and is advertised as a 3/4" offset. If you put the spring perches at a 3/4" offset, you put a bind on the front half of the spring (and you still don't get a full 3/4" of tire clearance). If you put the perches at a 1/2" offset, you put a bind on the rear half of the spring. The only way to not put a bind on the spring would be to set the hangers and shackle mounts at an angle to match the offset, so the springs would be angled and everything would be inline (eye bolts and shackles would be parallel to the springs, but the springs wouldn't be parallel to the frame). But that would set up an angle opposite of what you usually want, if the rear springs are splayed it's done so the fronts are narrower than the rears. E-bodies have splayed springs, the front is narrower than the rear. Like anything with suspension there are pros and cons to doing that way.