It seems that the "848" head was used on all 235s from 1956 and onwards. After 1956, it was also the replacement head for any 235 for any 1954 and later 235.

The "848" head's design results in higher compression (and thus, higher horsepower) when used on an engine that did not come with a 848 head.

The head could also be adapted to work on any 261 engine (which was available from 1954-1963). The 261 was always lower compression than the same year 235.