Hey man,
I'd be glad to answer any questions on the VG30, Im guessing your looking to buy a 300zx TT I owned one myself for over a year.
basically the overheating thing is an urban myth, as long as the cooling system is up to scratch, you will never have a problem with heat, As many track days will testafy.
They are just like any other car or engine, if the cooling system is blocked up then you will have problems, if its a new import, get it flushed and rodded straight away (like you should with any new import) then Just make sure it has water in it, and your good to go
Send me a PM if you like, Ill tell you anything you want to know