This really isn't a write up, more of what a "This is how I did it" type of thing. I may be making a write up if I decide to make a copy of this gun.
Internal shot. I cut the pump head off, and hot glued it to a metal rod I had laying around. The rod already had a hole drilled in it that fit the rod from the yellow grip from the front gun. I took that rod, and hot glued it to the bolt handle, so when you push the bolt handle back and forth, you pump the gun.

You can see the wire connecting the firing pin to little orange ring (orange ring not visible)

Orange ring that fires the AT2K

I hot glued the yellow grip to the sidearm for looks, and for something to hold. It's quite comfortable.

I took the little bar from the yellow grip of the front gun, and hot glued it onto the bolt handle of the Longshot. It doesn't reach out on both sides, so there is only on handle. It's still pretty easy to pump.

Whole thing assembled

Questions or comments? This seems like something that would have been done when the Longshot came out, but I couldn't find anything here on Nerf Haven.
I know I didn't take enough pictures, but if you want me to clarify how it works, I'll try my best.
Ranges These are a little inconsistent because of my darts, not because of the blasters.
Singled Longshot-
65'
68'
72'
80'
82'
AT2K-
55'
58'
59'
59'
62'
YouTube video with firing test:
Edited by Coop, 21 September 2008 - 09:22 PM.