What do you mean by torsion bars? Spitfire has coil springs at the front and leaf spring at the rear!
If you mean the front anti-roll bar, I am not aware of any good or bad suppliers. The only requirement to change would be if the bar is bent. The only way to do this is to take it off and look at it. It could be fitted the other way round if you think the car is "lopsided" as a result, but there are plenty of other causes of uneven ride height. Most often down to rear spring, but front springs, and front suspension alignment (shims, turrets etc) acn also be the problem. Look through previous posts to get all the detail.
Although it is feasible, I would look elsewhere for uneven tyre wear before blaming the anti-roll bar, unless the car has a visible lean to one side.
First suspect would be tracking. Even if the tyre place measures the correct toe-in, its worth checking that the two track rods are adjusted equally. Measure from the locknut (or centre of the trackrod end nut) to as close to the inner ball joint ("felt" through the gaiter) as you can judge, on both sides. The two measurements should be approximately equal. I have seen racks fitted with all the adjustment on one side, which will give correct tracking with the wheels pointing straight ahead, but will give incorrect tracking as the wheels steer. This can cause uneven wear of the outer edge of the tyre tread in one side.

Section : Suspension

Torsion Bars

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Torsion Bars

Torsion Bars