I would recommend that your friend gets rid of his ugly assed 300zx & gets something better......
But seriously, if the timing belt went & he was still driving it would have done some pretty serious damage to the engine......
When buying a car with that many km's on it the timing belt is the first thing you should check......
I'm not sure about where you are, but in NSW all 2nd hand cars bought from dealers are under a mandatory 3 month dealer warranty. Too bad that it was 4 months before it happened.....