Late 70's were a mixed bag from MC as far as engine/prop rotation goes, as far as I can tell. It seems Mastercraft MAY not have cared which direction they turned. Im sure they were not doing anything with the hull to compensate for the prop rotation anyways. CC didnt start doing this until 1982, and they had always used RH props on their direct drives, so they were a bit more mature in their design at that point.
Im not sure what youre planning to learn by popping the distributor cap, because as you state, the rotor will turn counterclockwise (regardless of engine rotation) on a running Ford Windsor.