scope mount

I bought a Remington 1903 03 A3, and I can see it had a scope mount, but I do not know what kind will fit. Teh three holes on the left have been tapped, there is an additional part added where the rear mount should be, it has a whole. I believe I see where a ring might have been where the barrel...

Excellent shape Mark 5HD with LaRue SPR-1.5 I bought this scope about a year ago and have only used it a few times. I took great care of it, so it still looks like new and comes with the box and everything originally included plus the mount. I'm selling it because I haven't used it for months...