This car is really amazing.. Unfortunately that this car has several problems that will cost you a lot.. I am not sure how much you would find the parts for but the things is that you are able to tune your car as the way you want.. and one solution if your car's engine is dead.. you better buy a new good engine such as Mustang Shelby engine but this will cost you a lot. There is a place for cars that are totaled .. and perhaps you can find a crashed Shelby or any such cars like that and buy its engine..
For the windows.. go to the glass shop and ask them for details.. and probably they can tell you where you can get cheap ones.. I think the Mustang windows is similar to the Trans AM but I am not sure about that..
For the interior.. there are good stores that can fix your total interior but perhaps it will cost much.. you might only need to do the seats there if it was ruined and the rest of the stuff probably you can do it by your own..
This car is a treasure!! so make sure that you take care of it and make it more beautiful .. the 1964 Mustang
and the 1969 Camaro are my best Classic cars..
You can always refer to Google to find more information.. wish you all the best and hopefully you enjoy driving it later..
One more thing..... Do not change the car to be more modern! the car is designed to be classic.. so make sure you keep the interior in a classic look.. but yea the thing that you can change from its original is as I said the engine and probably the gearbox so it can handle the more horsepower you get in the engine.. because I know a friend who got an old Camaro.. then one day the gearbox stopped working..