Have a Brno mauser 21h with claw mounts and an old scope in the rings that is adjustable for elevation only. Problem is that the rifle shoots to the left of point of aim. Can these mounts be slid either way in the groove cut into the bridge? Thanks for any advice.

Depends on your mounts. All 4 of mine have windage adjustment screws that slide a dovetail between the claws and the rings. Some don't have that adjustment. The claws themselves are always fixed, they are very closely fitted into the slots in the receiver.