Did you notice the stock rubber bushings had “hollows” above and below the through bolts on each end? Those provide the flexibility required when the body rolls and the body end bolt and the rear axle end bolt are no longer parallel. Replacing the bushings with solid , harder polyurethane material can cause suspension bind. That will increase the twisting moment on the control arm.
The best solution is spherical rod ends on each end of a tubular control arm. But rods ends can be harsh and noisy. A good alternative is to use the poly bushing on the body end and a spherical rod end on the axle end. Allows the required rotation, but minimizes the transmission of noise to the body end.
UMI has a proprietary “roto-joint” which is basically a softer, non-metallic substitute for a metallic spherical rod end.
If your application is primarily drag racing, using lower control arm (LCA) relocation brackets are ver effective in eliminating axle “hop”:
In General, an “adjustable “ LCA is not required. Can be beneficial if you have to move the axle assembly forward or backward for tire clearance. I like the Spohn components. I've worked with Steve Spohn to provide dimensional input for his designs, he has used my Formula for prototype installs. Extremely high build quality on everything he makes.
1994 FIREBIRD FORMULA
381ci all-forged stroker (Callies Stealth, Oliver billet rods, BME 2618-T61 nitrous pistons) - 10.8:1 - CNC LT4 heads/intake - Comp Cams solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74#/HR injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11 Pro-Street gears - AS&M headers - true duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP / 800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117 MPH straight motor