I had a similar idea I posted a while ago. I didn't go into detail except for my Grenade Launcher for Rifles. Anyway, nice listing. The attachments could be graphic edits or gun "hats."

My first post mentioning it. http://www.graalians.com/forums/showthread.php?t=1678

Second post about it. Details about a launcher attachment. http://www.graalians.com/forums/showthread.php?t=2341