Weaver had these rings at the very beginning of their scope production. The ocular lens housing was unscrewed, and the turrets were removed, the rings slid on, then the turret and ocular replaced. If you look closely, you will see the screws that fasten the turrets to the tube.
That's how their scopes were first mounted. I have had several that were set up like that. If you did it in a very dry room, the scope wouldn't fog up........hopefully.
Ted