It would be a Pachmayr Lo-Swing Side Mount. The scope is pivoted away from the top of the action to allow clip loading or use of iron sights. Another version made use of the pre-drilled and tapped holes in the receiver ring and bridge of the Model 70, without requiring additional alteration of the receiver.

Replacing the Pachmayr mount (no longer manufactured, but they sometimes appear on eBay) would probably add to the appeal of the rifle.