Originally these cars did have a different spring on the drivers side of the car. Have you changed the springs to newer ones or are they original? One can look at the number and size of the leaves in the spring to see that the drivers side had an extra short leaf. A friend with a TR4 had the same problem as you but with the left side on left side drive car. We found that the spring on that side was weaker than the other side. I gave him an old set off of my car and his car now sits just fine. I would suggest that you change out your rear springs if you have not already done so. If you have done so then you should try to swap the springs. But I really don't like that idea as I suspect that the one spring is weaker and therefore will bring the car down on that side.
Charley Fitch
