Ideally you would want to have a 1968 shop manual. I don't have one myself, but somebody here can probably help you out with the info you need. Here are some of the 1970 pages, I found them at Hamtramck-Historical.com, didn't see the similar pages for 1968 at a quick glance though, only the paint chip charts. (I think the info you need is on the back of the chip charts).