The key item is the barrel diameter under the sight block. A .700 barrel diameter with .750 sight makes for an issue mounting it up. The makers fix it ordering complimentary parts. those of us in the field discover it too late.
I tried boring out a pencil barrel FSB but the forging is smaller, it broke out. I shimmed a clamp on Armalite with feeler gauge leaf but later just gave up and free floated it. That sight is now on a pistol.
The whole concept is to maximize the sight length for more accuracy, but if you clamp on an optic then you defeat the purpose. Dissy's are suited for carry handle iron sight builds for a different look. Low pro gas blocks for midlength gas under rifle handguards work, the FSB anchors the cap, it's mechanically feasible. But it's all about the barrel diameter and sight block having the same dimensions. .050" off is a huge no go.