Here is a link to the page from the master catalog showing the 848 casting# for corvette 53-57.
http://chevy.oldcarmanualproject.com/1929_57chevyparts/57cmpc0136.htmMy 261 head casting# was 3836850 but it has lower compression than the 848 head.
Side by side comparison of the 848 head with others shows the smaller combustion chamber.
The shop manual of a 235 with non-848 head shows 7.5 compression ratio. The 848 head shows 8.25
A bored 261 with milled 848 head can give around 9.5 cr without further mods.
Mine came out to 9.3 and it burns lean and clean with 91 octane gas with plenty of torque and about 20 mpg on the freeway with a 3.55 rear.
