Not really, you will not be able to have a smooth swing and follow through. You need at least a 24 inch bbl and a 26 is a better choice. You also will find that different chokes can have a huge effect on patterns and point of impact.
A couple of yrs ago when I started duffer shooting clays I had an old resident 12ga 20" fixed IC Rem, it just didn't cut it. I went to a Moss 500 24" Accu-choke 20 ga (12 > 20, old motorcycle shoulder injury) which was better (less recoil, choke choices), but I still preferred the 12 ga. and wanted the longer 28" barrel. Bigrob, I think you did good with another Moss 500, a nice shotgun and the longer barrel is better for shooting clays. I chose another / different solution. Since I don't go out on the clay trail that often instead of a replacement 28" barrel for my old timer Rem I got a new NEF Pardner 12 ga. 28" vent rib pump. At $180 it was $40+ cheaper than the replacement 28" 870 Rem Barrel which paid for a skeet choke and a new recoil shoulder pad. Not as easy to use for double clays as it's action certainly is not Moss or Rem smooth but it is rain / mud proof plastic and I don't worry about it...still having fun with just a cheap knock around.