You are correct that the GCA of 1968 prohibited the importation of Class III weapons for individuals, however you could still buy UZIs or HKs or whatever that were converted from semi-auto by a Class III manufacturer until the 1986 act made this practice illegal. By the same token prior to 1986 you could buy new US manufactuered guns such as the M-16 which you can't now. So to say he did next to nothing to the machine gun community is a statement I don't agree with.
Clinton was President from 1993 - 2001. How do events that happened in 1968 or 1986 have anything to do with him? I have to agree with chetchat, Clinton had nothing to do with the supply of C3.