[BNaylor]

Basically CAIs from a similar GM "W" body car like Grand Prix should fit. The problem is you do not see many, if any advertised for a Regal LS. Plenty for the GS model. From what I understand a CAI from SLP or MSP for an L36 should fit but there are no guarantees additional fitting mods will not be required. The Regal LS has a L36 engine option RPO code.

For the K&N like an Aircharger contact K&N technical support and ask them which one will fit. Good luck.