Thanks fella's. I've begun researching the matter, and I believe that someone has replaced the rail with an optics rail. I played with the idea of putting a rear sight on the rail, but if I did, I would have to raise the front ramp substantially. I'll just try and order the OEM.
I tried this on a target to see how it shoots, and even without sights it "fits" me and I can do ok instinct shooting.
I just can't quite use a pistol scope for some reason, and it makes the gun too bulky for my personal comfort.
Ben