[Dave Goob Cook]

I bracket race a factory 4 link car, (Malibu) all bushings in the rear bars are solid except the upper housing bushings, pinion angle is critical, I MUST have at least 4 degrees negative, runs best at 4 1/2 degrees. Now how you measure pinion angle is a subject for much debate, but I measure relative to the ground and frame (at ride height) plane.
I feel like what makes the rear suspension work is the "allowed" pinion rotation of the upper bushings at the housing.
I get probably 4"+ of separation at the rear axle, or plant on the tires, however you want to look at it.
Atlas non-gas shocks on the rear, QA1's on the front.
My setup is the old Southside Machine deal, the lower bars point "up" at an insane angle due to being located low on the axle housing. Upper bars are near level.
Your long wheelbase is a bit of a conundrum, in my opinion, although your weight bias is much more favorable than mine. (1660 frt / 1440 rr empty)

The M/T "stick" 29.5x9 tires are the absolute WORST tires I've ever run on my car, I usually run only Goodyear D-4A Radials (at 16-16 1/2 psi) for warm tracks. (6303's)
I'd think that a stiff sidewall or radial slick would be the ticket for you.

1.37 to 1.39 short times at any track with decent air, 1.40-1.41 when the HP is low.
Of course, it's an automatic, 2.10 low ratio TH-400 with 5200 stall off the t-brake and 3600 two-step, but the "hit" is fairly solid. Had no trouble with the 2.48 low ratio though, just made the car feel better with the 2.10 ratio. 4.11 rear gears.

I will agree with others that some quality video of your car is mandatory to study what is really happening. Nothing like a frame by frame playback to see things you never thought of.

Don't think you'll ever see the potential of your car until you can stand it on the rear tires at launch.