If you need disc brake parts, forget a donor car. Most Mustangs, except for a few, like the GT had drum brakes. And they were manual disc brakes, so they didn't have boosters. Sounds like you are trying to do a conversion, try the above mentioned Granda swap, much cheaper, and the brakes are better than the old dual piston style calipers that the '65-'66 Mustang had. The heater parts are so cheap from Mustang vendors it's better to save your bucks and just buy new. For the A/C, most Mustangs of that era didn't have A/C, so you likely won't find one on a donor car.