Kurt,
A "high-compression" "848" head might have a 8.25:1 compression ratio (1959-1960). Other things like cams and decking a head/block might increase the ratio, but most likely not higher than 9.0:1 to 9.5:1 (Jerry would know the possibilities, not I).
120+psi compression +/-10 psi over all cylinders is excellent compression (130 psi is shown for 1959/60 235s).
I have never used higher octane fuel in my 235/261 engines. I do not think that either one has a compression ration of over 8.0:1 (1960 261; and my 1954 235 has, at the most, 7.1:1). I adjust the timing on my 261 using the "ping" method.
