Did a little research a while back:
3835913 head was used first on 235 1st Series 54/55 trucks and again on 235 58-62 cars (together with 848 heads).
3836848 head was used first on 235 2nd series 55 trucks.
I used to have a 913 head dated 1958, which confirms this casting history.
Anybody's guess why chevy used both heads for the later 235 cars.
A stock 235 - 913 has 7.5:1 comp ratio
A stock 235 - 848 has 8.25:1
