You don't want a small gap because it will reduce efficiency & economy, and will cause tuning related (spark timing) offset depending how dense the cylinder charge is (low density + small gap = more timing required) which creates a dangerous or inefficient curve depending how the tuning is done
It sounds like a grounding issue or a age-related issue. The coil packs are 20+ years old then its probably age.
otherwise I would unwrap the wiring and re-wire the grounds/harness and increase ground wire size and attach to multiple sites around the engine not just the one on the back of the head.
Also make sure you are using the correct plug
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