Hi Doug,
I'm not experienced with the Goodparts springs in particular, but might be able to contribute a few suggestions about general front suspension setup...
Have you had the car professionally aligned? With the various changes you've made, I think it would be a good idea to do so.
Often alignment shops refer to a catalogue of OEM specifications, though, so you'll probably need to give them some guidance what you are looking for.
For a street car, around 1/2 to 3/4 degree of neg camber is not uncommon with modern radial tires. Even a full degree isn't unreasonable, IMHO, although it will likely make the steering a little heavy at lower speeds. Much over 1 deg neg is getting into more radical race settings and probably will cause faster tire wear like you describe, although the car will go around corners like it's on rails!
Toe is also very important, should be about 0 to 1/16" toe-in with modern radial tires. On a street car, that's probably the more critical adjustment in terms of tire wear. But, a lot of neg camber combined with a lot of toe-in or toe-out might cause really rapid tire wear.
The other adjustment is caster, which is about 2.75 to 3 degrees typically on TRs (after the first 6000 or so TR4s, which had 0 caster, like all TR2/3).
Also, I don't think you need to be too concerned about having adjusted it a bit by shimming the top cross member. That's an acceptable way to "tweak" the front suspension of TRs: shortening the cross tube to induce more neg camber, shimming or lengthening it to move it more positive. The only problem with using this method to make the adjustment is that there is no way to precisely adjust each side individually. It will simply pull the shock towers together or push them apart (along with the upper/inner fulcrum mounting points), and might do so unevenly. However, with the other available adjustments on your car, it should be possible to dial in each side more precisely, after making coarser adjustments with the cross member and upper fulcrum orientation.
Also don't overlook the rear alignment, since that can effect front tire wear, as well. Other factors that can cause faster wear include sway bar setup and un-balanced (front-to-rear) braking.
Finally, some tires simply wear rapidly, due to softer compounds and some other desgin factors. I had a couple cars in years past that used Pirelli P6 tires, which are great for cornering, but only lasted about 20K miles (or less if driven hard). Those tires had particularly stiff sidewalls that prevented much tire roll, but made for a coarser ride and a lot faster treadwear.
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