I don't remember for sure, as it was almost 40 years ago. But I do remember making a oil pump to main cap gasket for a 273 engine, I built. I'm thinking I removed a factory gasket, but there was none in the replacement gasket set.
Edit: I just looked at the 1968 Factory parts manual. It shows a oil pump mounting gasket for the slant six, and the big block. It does not list a gasket for 273,318, or 340 engines
