I don't believe that GM factory castings with the same casting# were different from each other.
I compared all my 848 heads and they were exactly identical.
Btw: The difference from 8.0 to 8.25 cr would come from the type and thickness of the head gasket or as little as .02 milling.
The master catalog shows only two heads available for 1954-1962 235s:
3835913 with 7.5 cr
3836848 with 8.25 cr
I drove my late 235 daily with the 913 head for years until I switched to a milled 848 head a few years ago.
The differrence is noticeable in power and sound.
