I shot bullseye years ago in prep school and college and the ones I saw were all aftermarket. I guess it is possible someone sent a GCNM back to Colt and they installed it there. In that case I am not sure a factory letter would show that.
During the heyday of bullseye pistol shooting, Colt was a very conservative company and did not use uncontracted aftermarket parts in their pistols. Unless the seller is able to provide a factory letter or a letter from a Colt employee/executive stating that the rib was installed for a Colt employee, it didn't happen.
That's correct. He claims a rib with the extension front sight.
Searching the internet before this post I did see reference to the 80 Series NM made in 1991-1992 that did come with Bomar sights but not the top rib type.
I thank all for their input in confirming it is as I thought.
I will add this to the discussion. Back in the late 50s and 60s The Colt custom shop was basically farmed out to some little know gunsmiths of the names Clark, RL Shockey, and Pachmayer. A lot of these guns were marketed by a wholesaler Gil Hebard Many of these guns were highly modified with extended sights and possibly Bomar ribs. Some of these came in Colt Boxes as custom guns. Could A NM Colt have been modified with a rib? Possibly. Truman