Wow. I'm impressed. I think that might be the cleanest all original 280 I've ever seen. With good pictures, I can usually find fault or untruths in sellers statements, but on that car, at least from the pics, I can't find any. I can't find any evidence to contradict the claim of original paint, and it has been kept in wonderful condition. Based on the cleanliness, I assume that it was rarely driven in crappy weather, and was always stored in a garage.
Original paint, radiator and cap, master cylinder, windshield washer tubing, vacuum hoses, EGR is intact, original exhaust system, original frame rails, and the list goes on... Just look at that original yellow chromate!
Only things "wrong" are the sunroof, it doesn't have A/C, and it's a four speed instead of the five. I'd trade you for mine in a heartbeat. Even with all the improvements I've done on mine. In a heartbeat!
Congrats. My only regret is that you didn't pay more. I like to believe my car is worth more than that, and now I'm not so sure!
Now change all the fluids, put in new fusible links, and install relays for the headlights and starter solenoid. Also check that the radiator mounting wings on the upper sides of the rad are still attached. I've seen them come off before, and yours look a little flakey.