All M721's are drilled & tapped. There are plug screws in the holes, which are located on the top center of the receiver ring, and in the receiver bridge. These rifles use the same scope mount bases as the Remington M700's. Go on E-Bay and buy an older scope to save money and still get something better than a Trashco - I recommend a Lyman All-American 4X Perma-Center. There are usually several on E-Bay, and although older, they are still excellent scopes.

Of course, if you opt for a new Leupold, that is the best choice.....

The part the receiver (rear) sight screws to is called the "receiver". It is a separate piece from the barrel, which is screwed into the front of the receiver, called the "receiver ring". The bolt slides back and forth inside the receiver. If you look UNDER the arm of the rear sight that the peep is mounted on, there shuld be a hole or two with plug screws in them, just like the ones on the receiver ring. You will have to remove the receiver sight standard (the slide part that moves up and down when you adjust it for elevation) in order to remove the plug screws to mount the scope base. I don't recall offhand if the 721 has one or two screw holes in the receiver bridge. it has two on the ring, though. If it only has one in the rear, you will have to use a one-piece mount base,like a Leupold or Redfield Junior base.