Hey Tim,
Sounds like your half way there. You haven't mentioned what kind of tires your running. I suspect street radials? They will will spin on you. Drag radials will not spin on you, I guarantee it! There are 9 sec. cars out there on nothing but 9" drag radials.
Next is the boxing of the control arm... They WILL help. There is a reason that technique, and the parts have been out there for years and years. Those control arms are stamped steel and flex under torque, no doubt about it. That is a horse power/torque robber. The energy it takes to twist and flex the control arms should be used to plant the tires.
Now planting tires is a whole other topic, I'll try and keep it short but It will probably be long so grab a beer....
EVERY car and truck have something called an Instance Center I.C. On leaf spring cars it's where the front of the leaf bolts to the frame. Easy huh? G bodies have 4 link and it gets a little trickier. I want you to look close at this 3D graph I created. Its the actual IC of my 80 Elky just like yours. If you draw an imaginary line following both upper and lower control arms, you will see they meet in the rear of the vehicle. A HUGE flaw on GM! But... Ford F-Body mustangs have the same issue so don't feel bad
🙂
Now look at the corrected IC once you install Anti hop bars from Edlebrock
These measurements were done by myself and input in CAD so there right. So now you know what the hop bars are *really* for and what an IC is.
Think of it like this.. you have a huge refrigerator to push. If you push it from the top it will tip over, if you push it too low your wasting energy. There is a sweet-spot to get it moving somewhere below the half way point.
Adjustable uppers only fix your pinion angle, not your IC. There are different techniques to getting the IC from behind the car to the center where it belongs. One is mentioned and that's the Anti hop bars, they move the back of the upper arm *UP* thus moving that intersection. Another method is moving the front of the upper arm *down*, that accomplishes the same thing and I have seen kit out there that do that.
Finding the proper IC is still a lot more than that. First you have to find the Center Gravity CG point of your car. You accomplish that by weighing the front and rear and doing some math. (Maybe a sticky how to in the future!)
So to sum this up, and because we have identical cars I would..
first get some track tires
second box both uppers and lowers, steel is pennies if you have a scrap yard around and if you have a buddy with a welder your cost is almost nothing.
third is a sway bar
forth is fixing your IC.
What I covered is about 2% of the IC topic so don't think what I wrote is gospel. Do some research on yourself and ask questions. I lived what your living not too long ago and finally got my car to do what I wanted. Good luck!