I did plenty of testing and tuning with my Charger. All on the street though. A track would certainly highlight more flaws since things like oversteer seem to be exponential with speed!
From 1984 to 2002, I messed around with a couple of second gen Camaros. They used the same suspension as the same year Trans Am cars so I played around with coil springs, sway bars, different bushings, etc. When I got my Charger in 2000. I did the same thing. I noticed that the front sway bar was very close to the contour of a 73-76 A body. At the time, Dusters and Darts were still common in the wrecking yards. I took a bar from some Dart and walked the yard until I found a thick bar that was similar in shape. It turned out to be in a mid 70s Chevy 2wd truck! What ???
I took the 1.25 bar and cut the ends off of it, then had a shop drill the ends to attach the end links. At this time, nobody had the 1.25 solid bar in stock on the shelf. For approx $70 including new bushings, I had a custom front bar. At first I used a 1 1/8" rear bar from a Ford truck, only because it fit the car between the frame rails. The car handled pretty good. I had stock 318 leaf springs and 1" MP torsion bars too. It still understeered at the limit but overall it was better than stock.
I later changed to the 18" wheels and tires. The front tire is a 275-40-18, rear is a 295-45-18. I added XHD leafs and switched to a 1 1/8" front bar and a 7/8" rear bar. My thinking was that reducing front roll stiffness while increasing rear stiffness should balance the car out.
Wrong.
The car now oversteered too easily! Even when coasting through turns, the rear often felt as if it wanted to come around faster than I wanted. I tried switching the rear end links to rubber on place of urethane but it made little if any difference. It was fun to drift and mess around but the thought of a spinout on the street while trying to avoid an accident worried me.

Looking at the principles to balanced handling showed me that I had a bias toward REAR roll stiffness. I figured that a safer car is one that has a slight tendency to UNDERsteer but can be made to OVERsteer with application of throttle.
I currently have a 1.15" torsion bar. I REinstalled the 1.25" GM truck front sway bar, but replaced the 7/8" rear bar with a 3/4" bar (Frame hung) from a 1983 ImperiaL. This is the same bar that can be found on most Diplomat/Gran Fury Police cars.
This combination worked great....Until I replaced the tires! I had an 11 year old set of Nitto 555s and replaced them with the same size Nitto NT01s. The oversteer is back but not as bad.
Son of a beeeeech!