I've been told though I do not know for certain that the mustang headliner can be made to work but is really too short for a proper job. It may translate here to a one piece but I suspect it isn't exactly the right size.
I have been reading through other forums and it seems like mustangs to fear was pretty responsive to demand. Early they only offered 67 68 fastback but quickly expanded their line. I wonder how much interest there would be for 67 68 Cougars and 69 70 cougars....Chime in here. I know I could use the extra headroom and I am only 6' tall.
I would imagine there is no way to install one unless you have the glass out....so that would have to be a consideration as well. I had a LeBaron with a one piece and the fabric still became separated when the foam started to deteriorate.....so I'm still a fan of the bows, cuz it's way easier to fix after the fact.