I'm not that familiar with the Yugoslav 59/66's that were imported with mounts. I passed on buying because of the lack of available mounts/scopes. If I'm reading your post correctly, the rifle you now own is the one with the three screws, (two thumbscrews and a threaded stud), and the smaller round centering post at the rear of the mount? And, the mount that you're trying to use is the one with the forward single thumbscrew with the locking nut with the larger round centering post at the rear?
AND, the two mounts shown in the 2nd and 3rd to last photos are the ones presently offered? Am I close?
There is an old thread over on Gunboards.com that has a user that bought three of the Yugo M59/66 rifles with that mount. He was only able to find one of the ON-2 mounts and scope. He
MAY have one or two left? Dunno? May be worth a query? Here's the link to the thread:
http://forums.gunboards.com/showthread.php?285879-Yugo-59-66-with-ON-2-Scope-and-Mount-New-addition-to-my-Collection I'll look around a little. Hope it works out for you. What was the ON-2 system originally set up for? The reason I ask is the last pic in your post of the complete rifle still "over there" has the scope mounted almost mid receiver. Not quite, but at least 2" forward of where
your mount sets. Will that mess with what you're trying to do?
firstchoice