You should have four numbers. C8 could be a date code, which means Mar 68 or possibly (more likely) 78.
there isn't a stamping on the front lower left side?
Like this one?
the second set of numbers is the model number.
In that case measure the primary and secondary throttle bores. If 1-7/16" and 1-11/16" it's a 625. If all 1-11/16" it's about 700-750.