The build sheet was called a Gate Release and Accounting form back then. Very similar to today's "window sticker" in appearance with listings of the individual options and prices in line by line format. It was not what we think of as the vintage ROT sheet with number codes and I am not aware of them being hidden in the car. I think CTCI still has some available to members as provided by Lois Emminger.
I will post some pictures this weekend.