The mounts are going to be fine as long as they are properly installed, the accuracy is moderate at best when shooting sabots, the plastic seldom comes off precisely enough during the sight in for an accurate zero, sticking with the same loads will help some but the slugs are going to be inherently inaccurate. 50 yards as Dale stated will yield 2-3 inch groups at best anyway you slice it. I would look at a pistol scope with a fixed power of around 2 or 3, there are also some nice slug gun scopes as well. You can also have the reciever tapped for scope bases, which a good gun smith will make sure is aligned with the bore, this would be my first choice of action, unless the barrels are interchangeable as is with my Mossy.
WELCOME TO OT!!!!!!! Let us know what you decide and how well it works out for you.