I had the same problem for years. I tried mono leafs and Caltracs, but they were brutal too.

I consulted with Dr Diff, and he solved the problem of the buckboard ride. He told me to use two passenger side Super Stock springs, but this time for a 1968 a-body. They are the 2800lbs springs.

It worked. My car rides better than it ever has, sits perfect and hooks up hard.

1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)