I could be wrong, but I think I've seen other types of Buehler rings for sale on eBay. Maybe you could find a set of Buehler split rings and still use the existing base.
Rod
After a bit more research, it appears that what I really need is a pair of Buehler SPLIT Rings�just exactly as Phil99 suggested. Those rings should work with the exiting Buehler base on the rifle and would be compatible with a modern scope. Buehler Split Rings look this:
The rings I have are Buehler CLOSED Rings. And I still don�t know how they got the front ring on the existing scope (just bent it open?).
Now to locate the correct Buehler SPLIT Rings. Ebay!
Other viable alternations (with new D&T) would seem to include Weaver two-piece bases, a Leupold one-piece base and Conetrol two-piece bases, all with appropriate rings.
Aren't rifle projects fun?!