yea, from what I remember my C64 used composite video...that was modulated to RF. Then again I used a 13" TV as my C64 monitor.
I can't remember if they had a dedicated RGB signal or not, but I think even the "official" C64 monitor had a composite video/mono sound input. I can't see the point of a dedicated monitor as they only did the equivalent of about ~240i anyway.
Maybe there was a DIN connector or something, but I think there were only 2...one for the printer and one for the tape drive/disk drive (the disk drive was more expensive than the whole computer! You had to be RICH to have the disk drive!).