Timing

Killer6 said
To that end, My '66 383 with a closed chamber head & shim gasket defied detonation, I ran as much as 52° total with no vacuum....just to see. Had no top end but never pinged once, having squish &/or swirl is more of a primary factor, given the same quality of mixture.

Exactly. Every engine is different and they will require different timing curves.

Yours is a perfect example of getting the curve right for what the engine wants.