Inch pattern L1A1's had a bayonet lug as part of the flash hider.
The standard FAL combo device had a bayo that slipped over it. The "lug" was two milled slots on the hider itself. The bayonet has a tubular handle.
The G-1 had a lug as part of the barrel, although its primary use was to attach muzzle devices (flash hider, BFA, grenade launcher) notably Turkey made bayonets for them.
The long FAL hider had the bayo lug attached to it, to, akin to the M-14 hider/lug.
The early FALs had no hider, but had a plain barrel with the bayonet lug milled as part of the barrel. There were bayonets made for them that had two prongs on the muzzle ring, so that the two prongs and the blade of the bayo made a flash hider.
Edit-so most owners will be able to add a bayo lug to a FAL simply by changing the muzzle device to a hider. I would imagine that DSA and the like will offer these devices. One could also adda a Vortex or other flashhider with the correct diameter and get a bolt on lug (Bushhamster offers on) to make cold steel a reality.