I recently mounted a 42 mm BSA Red Dot on my gun using a Weigand mount for my drilled and tapped Gov. Comp. model. The slots in the top were not spaced correctly for me to mount the BSA without modification. I used a rotory tool to cut another slot in the top and now it works fine.
The picture of the MGW that Bullseye posted looks similar to the Weigand that I got where the slots that are close together are too close together and the slots that are farther apart are too far apart.
Weigand's no gunsmithing mount seems to have better spaced slots. Here is a pic:
Another option is the B-square mount:
I am sure that that would work, but it is quite a bit more expensive than the other options.
