When lifting the rear of a blazer..

[1969k10stepside]

I'm getting ready to put the lift on the blazer.4" springs up front and I'm going to use 4" blocks in the back..This ain't a blazer that is topless year round,it's actually used in the winter so I'd like it to not sit lower in the back while the top is on.How much do you guys think these old 4wds actually sag with the top on? Keep in mind these are factory springs,not lift springs.Do you guys think 4" blocks with a 1" add-a-leaf with stock springs will make it sit pretty level with the top on it? I'm use to lifting trucks,which don't have the added weight of a top in the back,or a tank full of gas to weigh the truck down either..