i am pretty sure the 5913 head was 7.5 or 7.8 cr, I cant remember which, the 55-57 (and possibly 58) was 8.0 cr and the 59-62/63 848 head was 8.5 cr. So not that much difference in cr between the 55 5913 head and a 56-58 848 head. Even today, I run across many more 5913 heads then I do 848 heads.
