Greg,

with 3 flats of preload in the rear suspension, which is a lot for a 4 link, that makes sense the car was steering left on you while the wheels were in the air. Since you scaled it with the preload in it, and then took the preload out of it, I would run the car with the preload where your rear corner weights are almost exact. Scales are crazy when you use them because as you can see, when you change preload, you don't only affect the rear corner weights, but all of the corner weights. How much preload do you have in it to get the rear corner weights that close? If you take the car back out with that setup and it still wants to push left, I would try a neutral preload, and if it still pushes left, you can try negative preload. I would put negative preload in it on the scales to see how much weight it moves around in the event you find yourself adjusting preload at the race track. At least that is how I approach my own. Also, do you have an anti roll bar on your 4 link?