Strange S60 Rear End Help

As long as you are even 1/2 way close on the perches you can use Degree wedges
(Shims) to adjust the rear end when assembled. I would have them welded on 3 Degree
down and adjust them from there when I assembled the car with your Superstock springs.

I use wet towels and keep the housing cool particularly on 8 3/4 when welding on the perches.