Did you resolve this? I am having the exact same issue. I have measured the distance between left and right sides at the rear mount point (Frame) to be exactly 27 inches, the middle (Axle perch) to be 27.75 inches , and front (Shackles) to be 27.875 inches and flared out.
For proper fitment it seems all mount points should be the same distance apart.
I am beginning to wonder if the axle perches have been modified from stock. I expected the axle perch separation distance to be the same as the rear mount points on the frame. If the axle perch mount points were widened it would cause this condition. If the mount points at the rear (Frame) is bent inward it could cause this condition. In both cases the only options for fitment would be the leafsprings bend laterally (unlikely) or the shackles flair out to compensate. Given the shackles are held in place using polyurethane bushings, it is likely the bushings give way before the metal leafsprings bend laterally.
Does anyone have factory measurements of the axle perch distance between left and right, and/or the rear mount point distance?
1983 CJ7 Laredo 4.2L I6 - Trying to remain faithful to stock restoration - "but its hard"...