Casting numbers for GM engines and heads are not a positive indentifier. The casting number was the part number of the casting (duh). Then, that casting could be machined into one or more part numbers.....like heads with small valves and another part number with big valves. Also, the same casting number is usually used over several years.....and several models of vehicles.

There is a stamped number on the sixes just like there is on a V8. The six number is on a pad near the distributor if I remember correctly. In that stamping is a two or three letter combination that tells the year, vehicle style, and (usually) if the car was a stick or auto. The code on a V8 also tells the engine horsepower (carburetor) and if it is a solid lifter motor or not.

dont know the site with six identifiers.....used to be in the paper parts books at the Chebbie dealer but that's a long time ago.