Regardless of chamber design try to establish very tight quench.
Steve may be onto something with that chamber design.
Many years ago I built a 460 Ford that had heads with very similar combustion chambers and it was extremely octane sensitive. Never really knew why because it was pretty low compression and very well chosen camshaft (towing application). It should have been fine on 87 octane pump fuel but we found that it required very conservative timing settings or it would ping everywhere, even at very light throttle openings and very light load.
That engine still led a long life and made PLENTY of power for what they were doing with it, we just couldn't run much timing on it anyplace and had to keep good fuel in it as well......Cliff
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https://cliffshighperformance.com/
73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile),
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