Man I'm in the exact same boat! When I got my TR6 there were none to found and bought one that had been in an accident. Supposedly it had been side swiped by a semi on the Left side. When I got it together it would not drive straight with out massive shimming in the rear and the front left sits low. Found the frame bent. Got the frame straightened, no change. Argued with the frame shop, no change. Found excellent replacement frame. When I had the old and new frame out I compared them and measured and could not see any difference. I traced them both out on a big piece of card board and could not see any difference. Scratched head. While the car was up on jacks putting the rear rear wheels on I noticed the rear wheel vertical angles were way off. I don't know how many times I've had it up on jacks and never noticed it but I guess I was just at the right angle. Pulled out the trailing arms and looked at them. The Right trailing arm was bent at the joints. Got replacement arms. Car now runs straight with equal shims BUT Left front STILL sits low. Last weekend I pulled front springs out, looks good. General inspection of parts, nothing seems bent. Replaced lower left spring pad with up rated 3/8" thick urethane lower spring pad. Still low. Need to check Right rear spring pads. I have a Rouge thick spring pad laying around (where did that come from?) Maybe I didn't notice I have thick spring pads in the Right Rear pushing the Left Front Down. The difference between the Left and Right Front is a little finger with a corresponding difference in the rear. Makes the driver look like he weighs 400 lbs and I don't **** it!
As a side bar. I got the trailing arms from another guy who I sold my old rusted parts car to. I thought I was buying my old trailing arms back but he said that my old trailing arms were cracked and he threw them out. I actually got another pair which supposedly came from an undamaged car. So, although the trailing arms may look beefy they may actually be rather weak. Plus with their odd shape it is hard to tell if they are bent.