Some general info on the Matchless-framed Nortons:
http://www.nortonownersclub.org/mode...id_detail.html
If it's indeed a '69, then it's most likely a P11 or Ranger. But I don't think that's it. The bike you're looking at is an N15 judging by the frame and the oil tank/side cover. That bike could be a '66 or '67. Maybe even earlier as it looks like it was converted to coils form the old magneto. Someone please correct me of I'm wrong.
Post up the numbers if you have them and we can check. Still, ask the guy if he has the original bars, seat (or even just the seat pan) and pipes/silencers for it. Those look to be the big non-original bits on it.
I paid $4,500 USD for my '64 Norton N15CS. But it was 99% original when I bought it. If that bike is well-sorted and running, $3,500 is fair. Of course, finding some bits (if you want to go back to original) can be tough.
Totally worth the effort, though. Great bikes.
You're going to love that front brake.