This is a picture of a standard 2+2 (apart from the sunroof). Look at the front end, overriders are the vertical additions to the bumper.
Datsun 240Z Parts, Exterior, Page One
Notice also the indicators attached to the bumper on the standard car.
Inner wings are the panels that come between the front wheel and the engine, i.e. each side of the engine-bay. Now you've said the car was yellow it confirms my suspicion of a colour change. The inner wings would normally be the body colour.
So with these things in mind (and with respect your limited knowledge) you need to be very careful. People don't normally paint these cars to change the colour it's usually following major bodywork to repair rust damage.
These cars can be very rusty and expensive to repair. Have a good search on this website - the word rust should get a few replies!
It may be a nice, well restored car but it could also be a car that hides a lot of problems (chassis, floors etc). With these cars mileage is not as important as body condition.
In my view to be worth £5.5k it would have to be REALLY good and require no work. Another thing to look for is flatspots in the carburation (hesitation and misfire). If it has this don't think it's easily fixed (or it would have been done).
I don't want to put you off a 2602+2 or any Z but be careful how you spend your money.