Hoot,
The 1st option I'd try is to get a #62 Weaver base and see if the holes in the recv'r line up. Then have one or two more holes drilled in the base into the recv'r and see if that will work. If the receiver is alloy, I'd want two holes. If it is steel, then one should be adequate... (A total of three...) You might have to file another cross-slot in the base to get the mounting right on your sight... (of course, I wouldn't drill any more holes until I see if it will be acceptable with your sight.)
Another option would be to use the existing bases and extension rings.
Grasshopper