I thought they might have a forth line on them like 67 did that said like "4LP" or something that designated possibly a 4 speed or Z/28 or just different trim.
Nope... Like Joe and Ed said, there's not option info on a 68 cowl tag.
Take a look at the 68 example
HERE.68 owners have to dig deeper and try harder!
check ebay. have him put what ever he wants on the tag.... just disclose it when or if he sells it. if the car is undocumented then it really doesn't matter what tag he puts on there imo.
And actually it doesn't matter that it even HAVE a cowl tag.... it's still a car and it is what it is. When the original items are gone, the 'originality' is gone except for what we can verify with our eyes and knowledge. Do you worry about putting the mfg tag back in your sweat shirts when you 'tear it out' because it aggravates your neck? 
Gary, I basically agree with what you said. Once it is gone, it is gone... So then, it is what it is....
But, no one has ever offered me $45k for my Class of 68 sweatshirt --with or without the tag.

Hotrod, my bottom line is this: A replacement tag is not the same as a replacement fender --even with the best of intentions. And in the end, even with disclosure, it will always raise doubt....

IMO, tell him not to waste his cash or time on the cowl tag....