As Superslab said, the Ford GT-40 that ran in '66 at St. Jovite and (and according to RacingSportsCar) also ran Mosport in '66 and '67; the Comstock Racing #94 car, was a MkI. So any MkI is legal for this series. The MkII and the MkIV, however, are not.
Having said that, the intent of this proxy was really to focus on modeling and racing the true CanAm cars; not FIA cars that raced in their event on Saturday and then signed up for a Can-Am race on Sunday. Same is true for the Porsche 917k. But, as it says in the rules, if it raced in any Can-Am event from '66-'74 then it is legal for this series.
Playing off what chappyman66 said, I would love to see someone do a McKee Mk10; one of my all-time favorite Can-Am cars; from a small team that, essentially, lived from sponsor check to sponsor check.... There was always something special to me about "the wedge".

Allan