Fully rifled barrels are for sabot rounds, and also hybrid slug rounds like Lightfields and Brennekes. Just don't shoot rifled slugs.

As for the mounts, I believe you will need rings and bases on that rig. I'm not positive about that though. If the surface of the cantilever rail is tapped, but has no dovetail slots, then you'll need bases, and rings that work with those bases. It's no big deal, they come packaged and labeled for your application. There may be a ring that kind of clamps itself onto the rail. You just need to check it out.

You want a driving gun, so I would go with a low-power scope, or just leave your dad's Simmons on 3x when it's your turn to push.