Hmm. We've solved one, ie factory air with 3.55, they shouldn't allow that. Explains the dealer fitment. Now the L31 M15, that is a real doozy. This was a definite "not available". L32, M15 and GV7 definitely, that was standard in 10/77 for a HZ Kingswood. If you can get me the VIN we'll check it out.