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Love to hear more about your ‘78 as I know you were looking for a nice one.
If you haven’t yet, it's worth trying Canada Vintage Services on for Factory Paperwork as besides Canadian built/sold vehicles, they also have info available for “most” '77 and newer US GM product, regardless of location built or dealer sold so always worth a whirl...
https://www.vintagevehicleservices.com
~ Pete
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