Tell Me about body lifts

[Kiss My SS]

I am interested in putting a body and suspension lift on my 72 Jimmy. I know all the ins and outs of suspension lifts but I know very little about body lifts. What I am curious about is, Does the body lift replace the original body mount donuts? Or do they stack on top of the body mount donuts? The reason I am asking is that my body mounts are shot and I figured that if I got a 2 in body lift, it would give me a little bit more clearance but would also improve the ride quality. Right now the body bumps the frame at the back due to completely rotted body mount donuts. If the body lift doesn't replace the donuts, then I will just go back with factory mounts. I found a place where I could get a 4in suspension lift and a 2in body lift for around $400. That would be plenty of clearance for some 35's or 37's I would think. Any help would be appreciated.