53 Cav, your engine is only 8.0 compression. Unless you have ungodly amounts of carbon buildup, then 87 is plenty of octane to run that. In fact, many lawnmower engines today use 8 or 9 compression ratio engines:
https://jackssmallengines.com/equipment/lawn-mower/Engines/ Though the max compression ratio without pinging depends on fuel mixture preheat, which would be higher in our cars than a modern small engine with its shielding and plastic intakes, it's still pretty comparable, and people generally report up to 8.5 compression being fine on 87. Point is, I'm not surprised that premium fuel is making little difference as to your pinging issues. I would start checking out TxGoat's list.
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