Carl, to your request to break Chevy/GMC out separately, here you go - people can just quote this post and it will grow and filter to the bottom (and pls insert new entries in order for the year, earliest-to-latest) - I believe some sort of text entry, a couple characters outside the quoted region will have to be entered as well to meet the minimum post requirement.
Please include last 8 digits of VIN (model year + plant + serial) along with build date (from blue door sticker or build sheet, no guesses!

)
Feel free to enter your last 8 = TBD, that way as the data fills in around it, folks can make an educated guess as to the correct month - but please only enter verified dates.
1967 GMC
1968 GMC
1969 GMC
1970 GMC
1971 GMC
1Z120204 = 4/71
1972 GMC
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1967 CHEVROLET
1968 CHEVROLET
1969 CHEVROLET
1970 CHEVROLET
0Z100986 = 9/69
1971 CHEVROLET
1Z602191 = 8/70
1Z622515 = TBD
1Z653085 = 4/71
1Z657051 = 5/71
1972 CHEVROLET
2Z153077 = 3/72
2Z168790 = 5/72