check out ksport susprnsions they have full bolt on air ride kits for bmws. for about three grand. other universal air ride kits would work with some fabrication. u may be able to find helper springs (little air bags) thaT go inside ur coil springs and u run a air lines to some valves and can fill it up with an air compressor. i used some from air lift back like 10 years ago. worked great and stiffing the rear up like a rock. they were like EIGHTY BUX