Maybe the definition and understanding for the term "bone stock" has changed over the years whereby it pertains to only mechanical changes but that has not been my understanding for that term thus my previous comments.When I hear bone stock stated, I take it as no mechanical changes. The very minor cosmetic enhancements the owner made to suit there taste are just that. The car was enjoyed like it was meant to be and obviously very well taken care of. Atleast that’s how it appears by the photo’s.
Back in the 60's and 70's when many of my fellow car buddies and I were purchasing Muscle Cars we used the bone stock term a great deal when looking at used HP vehicles.
Our understanding for that term back then and still to this day describes any given vehicle that is in the same exact condition as originally delivered from the factory and in this case from the Flat Rock assembly plant.
Again, if the definition of the term bone stock has changed to what you describe I was not aware of that change.