Not trying to start an argument, only a discussion so we can all learn. I respect your knowledge and your great NASCAR builds. NASCAR.com indicates:
GENERATION 2: 1967-1980
-Stock body with a modified frame.
-Modified chassis became part of the spot with Holman-Moody, Banjo Matthews and Hutchenson-Pagan building chassis for teams.
1967 FORD FAIRLANE
-Due to unibody construction on the stock vehicle, NASCAR allowed purpose built race chassis for safety.
https://www.nascar.com/gallery/the-evolution-of-nascar-sprint-cup-cars/#photo-1