Matt, I don't collect any information on '65-up trans stampings, but I can tell you that earlier ones had a variety of VIN stampings. Some plants used a gang holder and some used individual characters.
The statement that all plants used a gang for the VINs is completely inaccurate. The genesis for restamps was in the Corvette hobby, and by FAR, the most easily detected block or trans restamp is one that uses the small St. Louis font in a gang on other assembly plant components. (that's how their operation is set up and they haven't done the research to know what a real stamp should look like from other plants).
Verne