273 commando...

If it's a '67 and older engine, there is no way to prove for sure it's the original engine. You can only get close on the date codes cast into the block and the numbers stamped into the left front of the block. There is nothing to identify a 2bbl or 4bbl block or heads. They use the same castings. You can tell if the car came with a 2bbl or 4bbl by the VIN and/or fender tag.