Well just like posted in your other thread:
Eli: "Dude that's a PGI Mayhem rental from Tombstone! Mike Wood threw a bunch together for their old fleet."
Mutant Nova?
According to PGI you could order a Mayhem barrel receiver for any barrel pattern as part of their interchangeable/mix 'n' match gun component plan. Although it seems like they only did Spyder & AC...
Does that one allow you to change feed port location?