Thank you for the compliments. Both mag extensions are factory Remington.
The extension on the top shotgun is a +3 and the extension on the middle shotgun is a +2. I've had the top shotgun since 1989 and, back then, the bracket for the extension lacked the swivel stud to attach the sling swivels. I just left it that way, as I never slung it. The middle shotgun is a Police Magnum from 2004, and it came with the +2 extension. The new brackets have the swivel stud attached. Both extensions have functioned 100%.
I really dig the Police Magnum. I had the LOP shortened to 13", polished up the front bead with Flitz and a dremel, and worked the heck out of the action. It has a very slick action. Slicker than the old 870.