Their is enough Model 12 experts on TS if you obtain pictures will be able to advise you if it "real" or "faked". So many fake model 12 Pigeons were sold in the 70's, 80's and 90's by a few folks known to peddle these guns. Most Model 12 guys know who I'm talking about and these guns do surface again and seen them offered on the Intranet. While the stock/forearm checkering is unique, points on pistol grip panels, bottom of forearm checkering, Jewelling on bolt and shell carrier what's unique inside A REAL Pigeon grade is the polishing of the internal "guts". Winchester only had done these on this "Grade" while some fakes don't exhibit this feature. If you find a Model 12 Pigeon ask for pictures if the trigger group and underside if bolt as I'll tell you if right or not.
Personally, you have to fussy with some of the national dealers who have be known to peddle these pedigree model 12's.
As far as Barrel Extensions, they surfaced latter 70's, mostly 80's and 90's, no serial # while some had Pigeon's engraved on the bottom. These were called "lunch box" parts leaving the factory, as well as proof stamps too. I heard during the years of collecting model 12 some folks even had the serial # stamps too.
Personally, other than checkering, jeweling, famous Pigeon the only plus to a Pigeon is the "guts" inside of the receiver so my suggestion would be a standard grade Model 12 "target" gun, if for Trap, the 2 pin rib is a 'work of art", old timers call it "rough back" for pattern on top of the receiver. You can't fake a 2 Pin rib model 12.