Update 8/26/16
Finally resolved issue with ECS Tuning and they admitted their mistake and accepted their springs back while I got Suplex 06204 (OEM identical) at the meantime.
Did some research on Suplex and they're made in Germany and excellent quality. Suplex on right and ECS Tuning BMW spring on left with the finger pointing to issue of narrow top which would't fit spring pad:
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Suplex perfect fit both both pads:
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It took some work but I didn't have to compress spring which woudl be very difficult due to limited room. I was just able to push the whole arm down enough to slip the spring in:
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Spring pad seated and shock mount installed:
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Bilstein shock and 2 arms installed:
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All installed. No traces of air suspension. I have extra room under the tire (air compressor gone) now and I'll fabricate nice custom trunk fllor support over the spare tire since air compressor had that function:
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Things to do:
Install wheels, move car back and forth, bounce suspension and then fully tighten 2 control arms nuts and shock nut on each side.
Install trunk trim.
Alignment.
Done.