On my 67, I used a set of lowering blocks between the springs and the axle perches. It requires longer U-bolts, but is a fairly easy installation. I got the blocks and u-bolts off a parts car, so I'm not sure where they're available. Do a search on Ebay for lowering blocks... It came up with 188 items. Looks like they're available in 1/2" to 4".