Carl,
The gun you refer to with the check hook is the James Hayes 2nd Prototype Trojan. Serial Number 226709. It features the Hayes Revised cocking mechanism, experimental ejectors and a experimental forend latching system. This is the gun that I inspected and documented when I went to Remington. It is the subject of my Summer 2013 Double Gun Journal Article. And I will be putting together a more condensed version of that article for an upcoming issue of PP when i get the chance.
Actually, the gun was not locked up when I was there. it hangs right on the wall below the Trojan Skeet.
here are a few photos of that gun.
Parker Trip 109.jpg
101_0881.jpg
101_0866.jpg
101_0868.jpg
101_0871.jpg
101_0899.jpg