How do you get a Suspension to hook, when the track surface is marginal at best

Right off, I noticed your brakes aren't holding good enough when you're on the converter, and it's taking all of your 'wind-up' out of the suspension. It's removing all of the 'hit' on the tire. Not what you want on a strictly 'leaf' car.
It's a lower stall converter, and you're taking all of the multiplication out of it by loading it that high. Try leaving at 1500. It will shock the convert better and leave harder because of it.

Tire pressure is too low, the hide is practically rolling over itself.
If it's skating around on the top end, it's probably wobbling on the snubber.

Keep the springs, and throw on some CalTracs. The Caltracs work better with a softer spring anyway. Besides, the Caltracs reduce the springs function to just holding the car up, like a ladder bar car. Only with more tuneablility.
Buy the recommended Calvert shocks with it. John designed those shocks to work with his bars. cheaper too.
Pinion angle is less critical with the CalTracs. 3° down is all you need.

Defiantly check the diff housing. They're known to bend.

I've done everything stated here with the OEM 6 cyl rear springs in place along with the Calvert 'sliders' in place of the rear shackles. The car will practically hook up in a car wash on MT 295 DOT's.