I checked my chevy books and did not find a "CGO" , but did find a "CGC
.
Which comes up as a pass full size car from 1971 with a 350/with 245hp!
Clean the pad better and see if this matches up?? Most truck #'s started with a "T" @ TKO TGH and so on.
You can check the back of the block for casting numbers,and also the head casting numbers!!
It still a chevy!!!!