No question - the II is cool; seen it before. Leaf springs are about the worst way to locate a rear axle - and they're heavy unsprung weight. No doubt a properly located 4 link with
Panhard rod and coil overs will make a huge difference in both
suspension effectiveness and ride quality. However, that's a huge change and quite involved. And, you need to work with someone that understands the implications of how/where you locate the pickup points, instant centers, anti-squat/anti-dive, etc. Locating the rear end that way would also probably make you want to re-think your front
suspension - especially if it's still got the old 'twin-I-beam' in it -- almost as archaic and heavy as the leaf sprung rear.
I road raced a leaf sprung car, and we couldn't by the rules ditch the leaf springs. Two things I did that helped a lot. First - added a
Panhard rod to locate the rear end laterally. Lateral location isn't a strong point of leaf springs. Second, I varied shackle heights so the spring sat level with respect to the ground. This minimizes 'rear steer' when cornering hard.
If harder launches are what you're after (my car didn't have enough power to worry about that) then some sort of traction bar or control arm is probably available to limit or eliminate leaf spring wind up. There's a great article in this month's Car Craft (silver 71'ish Mustang on the cover) about rear
suspension design. Given what you're considering, it's probably worth a few bucks to pick up a copy.
