WELCOME.
The 'C' designation in the VIN indicates a 289 V8 engine. They did not come from the factory with the GT equipment group, or dual exhaust with that engine.
The photos reveal Power Steering pump, Power Brake booster, and the seller says the air cond compressor was previously removed. A nicely optioned model. I personally don't believe its value to be $18,500, but that's just my opinion.
Nice looking car with potential, but I'd want someone to personally inspect it. A lot can happen (deteriorate) over 46 years.
Neil