The front and rear wheels are different, that is not to say that they will not fit, however best to keep the rear wheels to the rear and front wheels to the front.
I have the original 18" wheels in stock if you have no luck with the breakers.
Alex.
Unfortunately the compression rod ball joint can not be replaced and you have to replace the complete compression rod.
I have brand new genuine Nissan compression rods in stock, and also low mileage preowned.
All good to go same/next day.
Just drop me a PM if I can help you further Chris:
Alex.
This should help.
It is really only a 5 minute adjustment from inside the car .
http://my350z.com/forum/engine-drivetrain-and-forced-induction-diy/477784-shifter-re-alignment.html
Preowned engines in stock and good to go same/next day: £1500.00
Why take the chance mate, best to fit a quality known brand, fully synth, 5W30.
Alex.
In answer to your question it is most unusual for head gaskets to fail.
More than likely it is just as the guys have said or it may be an easily fixed breathing issue.
I would not be to unduly worried with your findings and providing there is no oil in the coolant or the engine oil is not emulsified then I would be reasonably comfortable.
Perhaps you could use your findings to negotiate on the asking price.
Alex.