Engine casting number...3837004= 1955-57... engine head 383684 gm 28 = 1956.. The owner died and they had no info. on the truck so we do not know what was/was not done that's why all the research plus my buddies both own a 1948-50 3100 both of which are not stock and one stock 1954 150 miles from here. We are setting the truck up to look like 1954.