Howdy Back:
5 freeze plugs= 200. 3 freeze plugs= 144 or 170.
C8- C = decade of the 60s. 8= year. 1968.
Casting codes indicate an engineering change. They may be used in other model years then the one indicated.
5 freeze plugs were standard on 200 and 250 block castings. the 250 engine was not introduced until 1969, C9DE casting code. So your C8, with 5 freeze plugs has to be a 200.
Adios, David