I currently have a four inch lift on my 87 Jimmy with blocks in the rear and springs up front. I run 35's and have some rubbing. I am thinking of going to 36 or 37 and will be doing some more trimming than I currently have. I am looking at a 2.5 inch shackle flip for the rear combined with 4 inch springs and adding 6 inch shackles up front with my 4 inch springs. The shackle taking me up another 2 inches. I hear a lot of talk about 52's and 60's etc for springs. From what I understand that is referring to eye to eye measurement? Is there a junkyard or cheaper spring I can buy to get me the four inches I would need in the back?