I also have a good selection of original window stickers and also create reproduction window stickers for 1960-1970 Chevrolets. While most of us concentrate on the fonts which is usually a telltale sign of a reproduction document, I also look at the form itself. None of the blank forms sold by on-line retailers are exactly correct and more often they advertise forms as correct for vehicles or years they are not correct for. The forms changed through the years and sometimes even in the middle of a year. The Yenko Chevelle window sticker is not on a correct 1969 Chevelle GM form. In 1969 Chevrolet used the larger 8.5 x 11 forms for all cars other than the 69 Vette. This form is similar to a 69 Corvette form and absolutely not correct for a 69 Chevelle. If you reference Dale's very informative Chevellestuff site, he shows examples of original 69 Chevelle window stickers: Just scroll through: The Chevelle form changed to the 8.5 x 11 format in 1968.
http://chevellestuff.net/1969/misc/paperwork.htm
Paul