Don't believe anything, anyone tells you about an engine. We all heard the phrase "pics or it didn't happen" right, well in case of engines... 'papers or it's not real' applies. Get a cheap auto zone actron $20 compression gauge and test. If it's over 210 psi you will need better than 93 octane. My guess though is you will come in at the 160-175 psi range. I ran a high compression iron headed 355 for years on 93 octane fuel. It had 218 psi cranking compression. I did have to have the tune spot on though, timing pulled back, cool inlet air, 2 heat range colder plugs, jetted rich, etc. It ran for around 6 years like that on 93 octane before cracking #2 cyl. piston at ring lands. Now I run an 11:1 355 with alum. heads on pump 93 octane fuel, but this one has a bigger cam and only makes 205 psi cranking compression. Nobody builds a race engine using 76cc 400 sbc smogger heads.