I doubt that anything like that kinda information would be on the cowl tag or build sheet. The build sheet is your holy grail, but it will only give you the information of what your car was equipped with by the factory.
GM just didn't keep those kind of records back then. Canadian built cars (my 70 Chevelle SS was built at the Oshawa Ontario plant) have a better traceable pedigree, where you can send in your VIN and get a full built record, even without a build sheet. I'm lucky to have both.