The Stovebolt Site Forums The Shop Area Engine Shop How do you ID a pressure oiled 261 as compared to a 235?

I have run across an old junk 3/4 ton GMC with.....of all things, what appears to be a later model full pressure oiled Chevrolet engine. Hmmmmmm, I wonder what they were thinking? :-) My question, how can I tell, quickly, if the engine is a 235 or a 261.