Could never get past the extra hole.
If it had an extra, non-factory, holes in the receiver ring, I wonder if it has 2 extra, non-factory, holes in the receiver bridge?
It has a Buehler style replacement safety lever, so I wonder if it has had a scope mounted on it at some point in time. While the Buehler style safety lever would have been a useful change with any style of sights, it would have been necessary if a low mounted scope was installed. More questions than answers.
