Thanks guys. I see your points. But I would think a one piece Weaver grand slam base should provide a level surface for both rings. They come in quick detach as well. If one were to drill and tap the rib, It would seem to be quite a stable platform. I took a level to the rib (1/2 inch wide) and levelled the gun. I then took the level with spacers on each side, and it too reads level. (crude, yes), but is it precise enough to mount?

Are the mounting points of the bases supposed to be the barrels or the rib?
I'd be glad to post pics, If I could figure how!