That looks like a Parker Hale conversion, using a two piece Parker hale mount. Front base is secured by the two top screws. The side hole is the gas vent hole, not a mount. The rear base replaces the rear sight ass'y, so there are no visible mounting holes.
You will have difficulty finding them, as they are no longer made. You may be able to use a Weaver T-01, if the front holes are compatible. A third hole would have to be drilled in the rear receiver bridge.