I need to study up more on CWC bikes, but I think the A makes it 50 or 51, and there should be a small w inside the the C, as that's the Cleveland welding mark. It looks like they didn't stamp it very well or it was worn down somehow.
You've got a COOL looking rat there.Instead of hunting down all of the correct parts, I would just find a headbadge and leave it be. Great mix of parts = one cool bike!
Johnny