New guy from Pennsylvania

[Tector]

I have an 870 Police Magnum (used). I'd like to add a 2-shot magazine extension. But I'd like one that has a QD sling swivel stud (my gun has one on the magazine cap), and which includes a brace, or clamp, or whatever it's called, to clamp the mag extension to the barrel to support the extension. Seems to be a lot of options out there, but not like I've described. Any suggestions? Also, what rifle-type sights (open sights) are a good option? Thanks.

[Synchronizor]

By QD, are you talking about a standard sling attachment stud, or something fancier like a push-button release?