engine number stamp on the block

It looks like a VIN number, meaning it's 1968 or later, if I recall I read they didn't start stamping them with VIN's until after 1968. And yes that is going to be on the rear of the passenger side.

My 66 doesn't have a VIN, it only has the year/displacement stamping info stamped on a pad facing up near cylinder 1 towards the front of the engine on the passenger side as well.