Looking at a 68 GTS.......

68' is not going to have the vin on the fender tag. if the owner doesn't know where to find the sequence order number, and hasn't got it already to look at, be ready to do some digging. sometimes you can use an inspection mirror to read it from the back side, or take a rubbing with dark chalk on paper. that's the only way you know the fender tag matches the body. the best thing is have the build sheet that matches everything.
"1968 A bodies: Have the S.O. number on the upper portion of the driver's side radiator core support and trunk opening lip under the weather stripping"

my valiant's is under the driver side trunk WS just forward of the curved portion