The Longshot Front Gun is great for integration. It's functional space is small, and it carries a lot of dead space. Many people have put AT2Ks into their LSFG, but not with keeping the original pistol in-tact. This write up will let you fit both guns in the LSFG.
Here's your materials:

LSFG
2K pump and tank
at least 6" of PETG, or barrel material of your choice.
Start with opening your gun, and removing the fake barrel.

Drill out the AR in the Springer gun:

Cut the PETG and fake barrel to 6".

Wrap tape around the PETG, untill tight in the fake barrel.
Dremel out shown areas:


Place the 2K internals inside, like shown, and hot glue them in place:

The pump fits in there as if it was meant to.
Connect the firing pin with the trigger by any means possible:

I used Heavy duty steel wire (which is a bitch to bend and cut) and polycarbonite.
Screw your gun back together, and enjoy a pistol with the power of two guns. A pistol which is......handy

Thanks to Ace of Nerf for providing the LSFG.
Edited by Wes7143, 25 January 2009 - 06:55 PM.