The 848 head was introduced for the 56 235 car and truck motors. 261 truck motors used a different head. I have seen a few 848 heads over the years with casting dates in 55, and actually own one. But in every instance, those heads were cast later in the year, like late July/August through December of 55. I have never seen one earlier then July of 55. Those heads were all for the 56 model year (GM generally stopped production of the 55s around the end of August, retooled in September and began 56 production around end of September beginning of October).
Your head looks like end of June so there was theoretically 60 more days of production left for late 55 models. I don't know the lead time between the casting of the head, and the building and delivery of the motor, but my vote is that it is more likely a head for a 60. But hey, you never know.
