340 mismatched heads?

For a little perspective if concerned about performance...back in the 80's...

The pavement stock car racers in WI had come up with a lower cost 9-1 engine that lasted two seasons compared to the unlimited comp engines they had been running.

Tech crews used a whistler to check compression on one cylinder.

When the rule went into effect the tech guys found many engine bays had been modified so only one spark plug was accessible to check... Wires, oil lines, new tubing was cleverly placed in the way.

The engines were 12-1 except on that one hole which was 9-1. No difference in longevity... but you could hear which guys had the higher comp.