I run a 4" Tuff Country EZ ride lift, #14722K for 56" rear spring on my 82 k20 plow truck, rides really nice and no sag yet with the 8' western on the front. Nowhere near as back jarring as my 8" skyjacker all spring on the 86...hate that lift. They do recommend that you run the 14725K heavy duty springs for big block or plow though.
Separate note, a dresses 6.2l weighs about 1,000 before you steam clean all the oil off. I used a heavy duty engine stand for my BBC and did a mod on the turning part to rotate block easier. Got the crank gear box off a semi trailer landing gear and hooked up to the stand. Real easy to turn a block over or the whole engine over if you want and stop at any point.