This is were it gets fiddly, you need to slide the pipe into the barrel, then screw the lever to the pipe while it is in there.
I drilled a hole in the base of the lever, then screwed a bolt into it, cut it off to the desired length.
Inserted the pipe into the gun barrel, placed the lever down through the side hole and the tricky bit.....screw a nut onto the thread tight, so the lever is locked in place.
Trust me when I say, you don't have much room to play around in the back of the blaster.