Got the 60mm 300mm 100 kg springs in (11.9" 574 lbs/inch) in! With the height adjuster at bottom it sits lower than the OE spring on the other side. The car and as rolled up and down a small bump from road to drive way to get them to settle.
The Bimmer World top mount rear 60 mm spring perch requires round pin spanner wrench made for MCS suspension kit.
https://www.bimmerworld.com/MCS-Spanner-Wrench.html
When all hardware are added, OE spring is significantly longer than H&R 300 mm springs. It was already an inch higher just springs vs springs.
So if X1 springs were put in place of OE spring with new rubber hardware, it will be a good solution for M3 control arm induced drop to recover back to standard xDrive heights, or closer to it. It will work for sedans for sure.
If anyone wants X1 springs, let me know.
I expect the H&R springs to get less compression when loaded compared to OE springs. I'll raise them up later on next week and load up with wheel, tires, and dumb bell weights in the back to find out.
Also replaced one of the Bilstein rear dampers.
If anyone wants a new Bilstein B6 HD and willing to rethread, let me know. Just pay shipping.