don't need to take the guard off, although it does make it easier, use a mirror and torch and you'll soon see if you have, the two middle inlet tracks are stamped with a 2" 'R' and 'S'.
They were generally on all 182's, and quite a few of the later 172's. They flow much better than the standard inlets as the cast is not so restrictive. I have a set of upper and lower RS stamped inlets in the shed if anyone wants to buy them