I'm going to follow this along you journey. I just bought a 04 e53 with the 4.8 and the PO removed all the air suspension and installed Bilstein Sports with H&R Springs. While these are good o would rather have working air.
Is able to get all the old air suspension parts but haven't been able to figure out why is been removed.

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04 E53 4.8
98 E38 4.4
04 Touareg 4.2 (x2)
87 E30 (getting a 4.4/6spd swap)
89 E30, selling it
96 E36 parts car
MK2 jetta with a 1.9alh swap
90 XJ Crawler
2000 XJ crawler in the works
63 Ragtop bug
64 Bug
06 F-350 to drag all the above when they brake.