(note: I know Ø about the semi version of the M60)
All the 'fire control'is in the trigger/pistol grip assy on the M60. The M60 trigger basicly blocks or unblocks the bolt carrier from going forward ("open bolt" firing, if I got the terminoligy correct.. when the bolt chambers a round, it will fire.) very simple.(as long as the trigger is pulled, the sear remains down, Full Auto and "safe" were the only modes on this MG)
My SWAG is that they would have to modify the trigger assy to 'drop' the sear once per trigger pull. However, I would bet that something else would need to be done, cause what is to stop someone from using a Mil trigger group?
They were easy to maintain, biggest problem was the bipod legs getting damaged from users setting the MG up on the muzzle and the bipod vertically to do maint/field stripping.
I can see the attraction to having one, but having something that heavy for only semi auto?? in my oppinion, you could get yourself a nicer semi- .308 out of a FAL or M1A... then again, you couldnt feed linked ammo! (I guess the attraction would be a "bottom-less" "magazine"