Here is a 67-69 barracuda interior qustion for ya

the later seat back with a smaller soft plug has more of the skin exposed. If you have 67 seat backs with their larger sheet metal back covers, the 69 skins would work. You might have some excess skin to gather at the hog rings behind that metal back. The 67 skin does go some distance under their backs but I don't know how much difference there is in the frames/skin anchor points. If you wanted to put the smaller soft back plug for 69 on a 67 back frame, you would likely need to do some fabricating for its anchors.