I was working on the bayonet mount project, but stopped. I did come up with a super simple fix for the .223/5.56 AR with the carbine length gas system.
Bayonet Barrel Adapter for M7 M9 M10 and M11 Bayonets [BBA-1] - $14.50 : Tacticool22, Tactical .22 Rifle Parts and Accessories You loose a little blade length, but the bayonet does not rattle on the barrel any longer.
That Galil Bayonet Lug will be too loose (about 1/16 inch) until you put the retaining pin in.