it looks like someone replaced the rubber body mounts with polyurethane mounts. notice the grooves in the mounts, poly has 'em, rubber ones don't.
i replaced the bushings on my '85 crew with poly mounts a few yrs ago, and they are approx 2" high.
i have also found that all the square 4by's i have owned, that i never needed to lift the rear as high as the front, as the rear always sits a bit higher. i would check your front end, it may be a 6" lift.
i would consider swapping the 4" blocks for some shackle flips or shorter blocks, 3" is a tall as a block as you should run.
i have 8" fr springs with a 3" block and 4" flips in the rear, and it sits level
