I have the MI "Omega" 7" rail system on an old Bushmaster "Trunk Gun"
No gunsmith required, Free Float, and has 1" rail to cover the delta ring assembly making it an uninterupted rail system on the your top rail.
They've become so popular that almost every vendor that handles MI stuff is "Out of stock" for the moment. The rail system is top grade like any other rail system. Mil spec anodizing, 6062 aluminum, top shelf stuff IMHO.
www.bravocompanyusa.com usually has them.
I also have some of their sling mounts. Good hard stuff.
My KAC covers fit them perfectly.