The 848 head entered service in 56. The earliest 848 head I have has a casting date of like August or September 55 (I forget which at the moment) which was a production head for 56. But I also have a 5913 head with a 56 casting date (I took the motor this came off of out of a 56 car in 84 or 85) so there appears to be some cross over although I don’t know whether it is engine plant driven, or car vs truck, or maybe even for 55 stick vs manual trans or what the differences would be. As for using the 5913 on a later motor, I have a 5913 on a 235 I ran for quite a few years on a 57 block. The original 57 head developed a crack so I used the earlier head. Worked fine. Might be the case with the one you are looking at, installed as a replacement.
