I present to you, the KAC Swordfish!
Doesn't exactly fit, but the barrel position and top rail are the perfect distance. At the moment there's no way to secure the front end to the gun. There needs to be some spacers for the claw mount to grab on to and secure to the top rail.
I would also have to remove the outer barrel or cut it to get the front end to butt up against the rails. Plus the inner barre would be too long and would need to be cut down.
Aside from that, I think it would be pretty bad-ass!