I have a '67 with a 390 4bbl and 4 speed trans, I used the old school method. I cut one coil from each side, and with the slight sagging from the old rear leaf springs I had the look I was after. The tires set in the wheel wells so the gap between the tire and the wheel well is uniform all around. Since then (40+ years and 30K miles) I have had no issues except a scrape or two on some entrance ramps at businesses, the ride and handling is as good as original.
Rick.