I think the keys and ecus are coded for the NATS, nissan anti theft system. Nissan can programme them but not sure on the Elgrand key, having said that, I think tuners can switch the system off.
Will the Elgrand run right as its map is obviously 350z specific, cam timing, fuelling, ignition etc?
Are you near any of the tuners, Horsham or Abbey, may be worth a trip to them with a 350z ecu.