Like Blazin said, You have to do it so it looks right to the eye.
These trucks didn't seem to sit level from the factory. To me they look like the rear wheelwell is too low.
This can become more obvious as the trucks get older and the rear springs sag. Lift kits that use new front springs and blocks on the old sagging springs only make the situation worse.
When I put the lift in my truck I had a hard time getting it to sit right.
I swapped in 3 sets of front springs trying to make it sit level, it just didn't look right to me.
I finlay ended up using a 6" rear spring with a 4" front spring and had some spring shackles made to level it out. It's just a way to fine tune it to get it to look right.
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