I am surprised there isn't a dedicated tutorial on vinyl tops on this forum. If there is I haven't seen one. Do google search; there is info online about this elsewhere.
Coinccidently, I actually did a 66 GTO adding vinyl top. I used masking tape and made a thin strip of styrene for the chrome trim at the bottom of the sail panel seperating it from painted body.
I'll try to get a picture on here.