Mustang 65 v8 ?
I would check the VIN number on the car to find out what is original to the car. Most cars of the early 60's did not come with AC if they had the 4spd trans. A 289 4barrel could be a "K" code and 4spd would be worth a lot if it is original but the VIN will tell you what is correct. It sounds like it was modified and is not all original if that is what you expect.
6K is maybe ok but the car sat 10years, you will not only be replacing the fluids but the brake system will be shot if it's original drums, the old wheel cylinders are shot. The gas tank will need replacing alone with fuel pump and filters. The sediment in the tank will cause a lot of problems trying to run it. And that car will need to run on PREMIUM fuel to run correctly. I would replace the point and condenser with a PERTRONIX IGNITOR. Also the radiator if not full of anti freeze will need flushing and possibly the heater core is shot too. You have a lot of work ahead of you but take your time and it will work. Plan on spending a few grand to get it road worthy.