I own one as well. The D&T is factory if it's on the side of the receiver, it was made to fit a Weaver T1 mount with a Weaver 330 scope.
There were three variations, two came with the scope and the other just wore a Reising M50 rear sight.
I have both the rear sight and the mount on mine, currently using the scope on it. At first I was having feeding issues but since I started using CCI standard rounds in it it hasn't missed a beat.
Saw one on the EE here posted at $1500 a few months ago and it sold in around three days. I guess only having three hundred of these ever made brought a premium.