The 848 head entered service for the 56 model year on the passenger car line. The earliest 848 head that I have has a casting date of September or October 55 so for the 56 production year. 54-55 you commonly saw the 5913 head. What does the valve cover look like? 54 was first year for perimeter screws for the valve cover as opposed to the earlier center studs. Those covers also had four small slots punched into them for venting, and a nonvented breather cap at the front of the valve cover. 55-58 covers used the same four screw attachment, but no venting slots and a vented cap at the front of the cover. Later covers had the cap in the center of the cover. So if you have a non vented cover, that would be consistent with the parts mismosh.
Just up uploaded a pic of the valve cover. It does have the 4 vented slots and the none vented breather cap.
