I measured the Emblem location for you. The lower edge of the GTX is 9-1/4" up from the lower edge of the panel. From the door opening (front of quarterpanel) 10-1/2". On my car the stripes are measured at, 11-3/8" to the TOP of the TOP stripe from the lower edge of the rocker panel.
I wouldn't get to hung up on the stripe measurement. I'd center the stripes on the GTX emblem.
Here's a link t a E-bay item, 68' GTX with LOTS of picturres of the emblems and stripes.Dave
http://cgi.ebay.com/ebaymotors/ws/eBayIS...RK%3AMEWAX%3AIT