I used the 456/457 MP SS springs. They lost their arch and quit working after about a year. They did work well to begin with but started wrapping up horribly.

I went with Cal-Trac split mono's and happy so far! The car wanted completely different torsion bar setting and leaves smooth and level now.

'63 Dodge 330
11.19 @ 121 mph
Pump gas, n/a, through the mufflers on street tires with 3.54's. 3,600 lbs.
10.01 @ 133mph with a 250 shot of nitrous an a splash of race gas. 1.36 60 ft. 3,700 lbs.