I wanted to add about 2" to my 85 Crew cab. What I did was use the soft ride spring from Sky Jacker on the front. I think they called it a 1.5-2.5 lift. A much better ride than what I had on the front.

For the rear I used the blocks from a 92 W250. These are 6" and used my original rear springs.

I know this isn't what you are asking, but its how i did mine.