1st and 2nd only applies to '55. The engine serial #, which is stamped next to the distributor, and the block casting date, located above the starter, will verify the engine as far as year. I beleive the main difference between 1st and 2nd on the full pressure 235 is the water pump mounting. The 1st has the pump mounted partially over the head, the 2nd is only on the block.
