Jason -
What's the build date on your car? I have a friend who has a complete set of DF rally wheels all with the same date. All four wheels are stamped K18 7 16 DF . The problem is he knows they're rare and wants big bucks for them. He also has a complete set of XG rally wheels (stamped K18 5 8 XG and a complete set of DG rally wheels (no date stamp) if anybody is looking.
Paul
The later 68 DF's dont bring as much money as their earlier counterparts, especially the 67 or real early 68 wheels with the inverted DF only by the valve stem hole. I think that there is a big misconception out there that any DF wheel is worth Big bucks.
If the dates are July 16 68, they may not have even went on a production 68 z/28 and may be a service replacement wheel. That would lower the value, IMO