the oem ones on mine lasted to about 150, before the front started getting floaty and the back rubber started leaking and the constant running took out my compressor. if your elc still works you dont need the air kit. just those oem replacement struts for the back. which is the same part i posted but you would just hook it up like stock.
as far as the knocking you will have to take a look at what seems loose or contacting something while some one turns the wheel. might need upper strut mounts, in that case might make more sense money wise just to get the pre assembled ones, because those come with the mounts
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock