Partially true. I have read (and will most likely do this myself) that it is recommended to find a 280Z tachometer and at least install that, as the 240 tach gets to be fairly inaccurate with age.
You can also ask these questions at:
ZCAR.COM | Datsun - 240Z 260Z 280Z 280ZX 300ZX 350Z - Nissan
HybridZ