Any one know how to mount some optics on this rifle?

My brother is trying to mount a Burris AR 536 scope on his MR1.

Rear sight can be removed, but the mounting rail does not extend to the rear far enough to get proper eye relief.

I can't seem to google any other rails or mounts for this rifle.

The rear sight could be removed, which leaves 2 screw holes to help mount something. I was thinking if the rail was removed, someone would have already made an extended rail that used those two sight screwholes. I haven't found one. Help!