Weig-a-Tinny dril less scope mount

[Major Tom]

I have a mid '70s S&W 29-2 44mag. I would like to mount a red dot scope on it using the drill less Weig-a-Tinny mount. Video showing how to install shows them using 3 mount screws. Looking at my gun I can only see 2 screws holding the S&W rear sight. Is one hole covered? Or?

[lyman]

is the rear one where the elevation screw is?
some mounts have the small square based nut and a locking screw, that replaces the elevation screw (uses the factory nut sometimes)

[Major Tom]

Thank you lyman. That was useful info!