I wouldn't touch the chamber length. I have used 2.5 inch shells for everything from skeet and sporting clays to game birds with never a problem if I put the shot where the target is. RST makes a large selection of shells suitable to your new Parker.

I wouldn't alter the chamber length of an original Parker Skeet gun. In my opinion there is no valid reason to do so and it is likely to reduce the gun's value.... but hey, it's your gun.

Thanks to all for your replies. Looks like an order to RST is on the horizon, for 2 1/2" ammo.

I would not touch it at all.

Once you use the RST shells you will keep coming back for more.