225 Redhead!

Do the valve seats need to be hardened in these older heads if one is planning to run unleaded pump gas? Another question, this may not be true, need clarification, heads with spark plug cups were earlier years-non hardened valve seats, then when the head changed to the closed spark plug pocket, those were early '70's and had hardened valve seats, any truth to it or maybe the change did not coinside with the hardened/non-hardened valve seats.