In '68 the marker became mandatory by federal regualtion, the C8xx stock fender. Which is different than a '67 due to the marker light hole and formed mounting flanges. (and on some running horse bagdes the pin size and locations changed in '68 as well)
I just thought it odd that an undrilled '68 C8 part somehow becomes a 'C7... as all '68's have the marker lights. As such, it can't be the same as a stock 67 fender, GT or no...