Cooler heads always prevail.

I am going to make two recommendations.  Look at the VIN on the pillar.  If it is attached with rosette rivets and it doesn't appear to be glued on then check the frame number.  If the numbers match then you have a 68 with wholesale changes.  There were no convertables for the later C'3's so at least some other parts of the car are probably 68.  The birdcage for one is not interchangable with the coupe without fabrication work.