I didn't know this either, but learned from corvette guys that although the casting numbers were different, the heads were identical to the later 848 casting with the same compression ratio.
1954 was the first year this higher compression head casting got the 3836848 casting number.
The 29-57 master parts catalog also shows the 848 head as replacement for 53-57 corvette 235s.
These later heads also had more nickel in the alloy, which may have given them a different number. Just guessing.
