Could anyone tell me the year of an engine with C670321 stamp to the generator stand. Haven't seen one like this before, thought they were usually just numbers.

They all had letters before the numbers after 1300s started to differentiate the different models and capacities.

Is it definately a C?
probably a restamp, the amount of new universal blank blocks out there now is getting more and more common.

C was never a commonly used air cooled engine code.
I've heard rumours that C was an optional low compression 1600 in late 60s busses overseas but no one has ever come up with actual proof of that.

Can you get a pic of the actual stamping?

Definately a C. Gave that area a cleaning with my shirt to make sure of the numbers. Don't have a photo of it (annoyed with myself about that one) just wrote the number down of that one and another engine I was looking at.

A 'C' engine code was originally a 1600cc Transporter engine (44 DIN hp), made from 1967 to 1970. So it would have been a single port engine originally.

All VW engine codes can be found here:

http://www.clubvw.org.au/vwengines