Barrels are interchangeable on the 1187, so yes. Also Aimpoint makes a RDS that clamps onto vent rib.
As much as I don't care for the aesthetics, those side saddle shell carriers are really handy. Spent lots of time with the 1187P and dummy shells loading from a
Brown Coat Tactical carrier, to the point that I became 100% convinced of their utility. I ordered a 4-shell version to try on this SG.
WML - check.
Side Saddle - check.
Sling - check, but only to be attached as needed.
This is how I'm envisioning the setup right now.