Currently and for the future my car is setup to go quicker left or right, not for launching. Air bags are out of the car now. For several years I just left them install but squeezed them until collapsed, negative pressure, enough that they didn't contribute anything to spring rates. Separate air lines to each makes that easy enough.

Couple other things for the 8 1/2. Are you doing LCA relocation mounts on the rear? It's another plus, tuning tool. The angle of the LCA can effect several things, IC being the big one. Anytime you change the ride height that angle will change. There are bolt on and weld on relocation kits but didn't like the choices and made my own, while the rear was still in the car. More about that later if you need to go that route.

The height of the spring seat on the rear for the pigtail is short, adding 3/4" to the height is a good thing. All the 8 1/2 G rears had short seat height, GN and 442. Softer spring rates and longer free length rear spring got away with short spring mounts. On the SS 7 1/2" they double up on the seat height, higher rate and shorter free length. The cup used as a upper pigtail locator was welded to the SS rear's spring seat to make it taller. A cheap fix for GM. A quality piece of 2 1/4" exhaust pipe will weld nicely to the mount to make it any height you want. I had extra cups laying around and added them later, with the rear in the car.
The name of the game is you don't need coil springs popping out of their seat.

Truetrac, was that you only choice? I run one mostly for it's better street habits and hopefully better at the autox, not for drags. Have no issues with it at all but if the car was drags primarily or straight ahead blasts I might think about a locker with the correct springs in it. A spool is out. The Eaton posi I had initially in the 8 1/2 newer gave me any trouble, and it was exercised many times. The Truetrac replaced the Posi because i felt the Truetrac's "torque sensing" drive would make my car a little easier to drive. And I got a SUPER deal on all the new build parts.

I installed a Quaife diff in my son's hillclimb car several years ago, amazing how much quicker it was in the corners. Quaife, Truetrac, Torsen all helical diffs.