Look at the model numbers of the complete shotguns, they show whether they're SB1 or SB2, as Billy said, the SB2 10ga shotgun frame isn't the same as an SB2 rifle frame, only 10ga and 12ga USH barrels can be fitted to the SB2 shotgun frame. At this time they won't sell the Ultralight shotgun barrels as accessory barrels, they only come on complete shotguns. That leaves the 20ga USH or the 12ga Tracker II which comes with sights that can be fitted to an SB1 frame, the 12ga Tracker I smooth bore which is no longer made had a scope rail, and just in case you're wondering, you can't get a scope rail on Tracker II 12ga from H&R, but a gunsmith could silver solder one on as H&R did with the Tracker I, Warne makes a steel base that will fit, H&R won't drill and tap a 12ga barrel.
Tim