Isn't this a 3x magnified optic? If so, you can't co-witness your BUIS.

As far as sights for the OR gas block, it's on the same plane as the rail so you will want standard sights. Stay away from "gas block" height sights as they are for gas blocks that sit on a lower plane.

Troy, Sampson, Midwest Industries and YHM are all good options for a folding front or fixed front sight.