Not meaning to skew the conversation, but why did Europe use smaller blocks / bore size? Was this all European countries or a select few? Was it because of a perceived safety issue, governments wanting to legislate or tax based on emission or fuel mileage, etc.?

I saw the note about them in the recent restorer but it didn't seem to give a clear reason.
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Aaron in T̶a̶c̶o̶m̶a̶ Meridian, Idaho
(although still a Montana hillbilly at heart

)
1931 Coupe
1931 slant window sedan