Installed custom fabricated 3" lowering blocks on the 10 bolt rear end, ('81 Camaro) on my '50 3100. I'm using the original leaf springs. I've replaced all of the bushings...nice and tight. As you are probably aware, the leaf spring pin is not centered on the spring. To maintain the original wheelbase, 116", I had to have the blocks made so that I could properly locate the 10 bolt and still utilize the leaf pin for "securing" it if you will to the axle. I fudged to 117" since I'm going to 18" rear wheels. I prefer to maintain the original look as far as wheelbase.