Power windows
Power windows will require different window regulators. The motors are attached to the regulator and, of course, there is no provision for a crank handle.
Also, the door glass is different for p/w cars since they have a semi-circular cutout along the bottom edge to clear the window motor.
The entire car's wiring harness will be different too. You have the feed wire (engine compartment) harness, and the in-car carness which goes all the way back to the taillights...
To go with a factory setup will not be cheap, since the motors/regulators go for big bucks since they also fit the Mustangs. I saw regulator/motors asking $200 each at the big Spring Swap this year in Columbus. Then you're still stuck with the wiring harness issue, the switches, bezels,....
I do have a complete p/w setup for a 72 that I'm willing to part with, but it is gonna cost you! I have everything. The 'special' door glass, the four motors/regulators, wiring harness, all four interior bezels... Im having a 'clearance sale' on my Cougar stuff I've collected over the years, so .....
e-mail me if you're still interested.