When I bought my 75 Jimmy it already had blocks in the rear. They look like about 2.5-3in blocks(havent measured them yet). It sits level now with negative arch front springs. Am I going to run into a problem when I go to lift it? I was planning 4in front springs and shackle flip in the rear. But the way it looks I guess that I will have to get new rear springs also. So why not go 6in ft springs and 2in new rear springs with the shackle flip. What do you guys think?