Compression ratio too high for 91 octane?

Then there's no way to answer the question. Can he give you a cranking compression number?
Come on, now. There is NO streetable cam that can accommodate 11.8 compression and iron heads. Whatever cylinder pressure that may be "bled off" at low rpms that may reduce detonation there.....will certainly come back as the rpms climb and the cam comes into it's operating range.
I had 10.8 with aluminum heads and a big cam and mine still knocked on 91.