That'd be damn near impossible with a 'vert due to wheelwell intrusion into the 'vert top well... That is if you ever intend to lower the top! Otherwise, it'd be similar to (but NOT the same as) a Mustang. You're looking at a custom installation. The right person with fabrication skills and a MIG welder could do it.
Of course being a cougar doesn't help with anything coming as a "kit". I'd try looking at Alston/Maer/Fatman and see if they have anything that could be adapted though...? On a '73 I hav no idea what would come close though....take some really good measurements and