Do some Googling on "How to install a vynil top" and you'll find good stuff like this...
Vinyl Top Installation - A- Pillar Install - Mopar Muscle Magazine
It's not for a mustang, but they're out there. This article will give you a good idea on it's complexity. The following info applied to my 67, but might be something to think about. If your car was a vinyl top car originally, someone has puttied the rear trim holes over and you can find where there were at by looking from the trunk for the rear most holes, but the forward most holes will require removing the headliner in that area - yuck! I suppose you could locate the rear most hole through the trunk and use it and your new trim pieces to locate the others, but you will still need to access the area behind the head liner to get the fastenters on. I am assuming that the vinyl top trim attached similar to my 67.
Hope this helps.
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Ride On,
Noel
"I'll fix it or break it, Guaranteed!"
My Garage - 67 Mustang Coupe, 67 GTO, 67 Sprite, 72 Chevy PU, & Old Ford 8N.