Plant code
 

Over the years I have had 2 or 3 drivetrains that had a U in the vin. I'm told its possibly canada but cannot verify. All the cars were 60s built.

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More necessary to confirm your circumstances but GM has used digit U as a Plant indicator for Hamtramck/Detroit.
:beers:
~ Pete

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During 1966-1970 Full Size Cars were built in Lordstown, Ohio amount others, these cars all had a “U” plant designation in their VIN.
See Warren’s site, scroll down to plant assemblies:
https://impalas.org/numbers/

Thanks for replies.

Were those drivetrains big blocks?

One block was a #406 67 396 , the transmissions were both muncies.