I unscrewed the gravity feed neck from my outkast sniper II and put the 90 degree 3/4" elbow right on. Fit perfectly. Then I used a section of PVC pipe about the length from the feed neck to the back of the the bolt (doesnt stick out behind the marker).
Now for the ball gate I had to get creative. I couldnt find a shop that sold a ball gate and buying the CCI tube with ball gate seemed stupid if what I was trying to do in the first place was save money. So I took a section of another 90 degree elbow (cut so that it was straight) and put it at the end of the tube. I then took soft plastic (like that found on the lid of planters peanuts) and rigged a "ball gate" of my own and taped it to the end. It works pretty well. Looks ghetto...but it works. Lets the balls in but doesnt let them out.