You basically need to removed your safety, and insert this "L" shaped rod that has a slight bent in the long section, and a notch in the bottom that goes into the safety.
On the pump arm, you add two screws/bolts that attach to the arm that keeps the rod in place and moving back and forth.
It is the exact same setup as any sheridan pmi gun out there, as the sniper is a sheridan gun.
I'll try and take some pictures as I have a few of these kits lying around.
As to make one? Hmmmm.... I'm not sure I have a tutorial, but all and all it seems simple enough once you have the right tools and pieces.
Let me see what I can dig up for pictures, and the like.