06 f350 rear end drop

[2009pete]

I have an 06 f350 srw that I recently replaced the stock 18" wheels with stock 20" wheels. I was able to do it without leveling kit in front. I would like to drop the rear suspension to level the truck to lose the 1" that I added in tire hieght. I pull a 5th wheel camper and don't want to have to put a lift on it to tow level. Is there any reason I can't put shorter blocks in the rear suspension to drop the desired hieght? Thanks in advance, Rick