The VG30DE engine in the 300ZX has several differences compared to the VG30E engine in the Z31, including:
- Different mounting points
- Different intake and exhaust manifolds
- Different electrical connections and sensors
- Different fuel injection system
- Different ignition system
Due to these differences, it is not possible to simply swap a Z31 engine into a 300ZX. Significant modifications would be required to make the engine fit and function properly. It would be more practical and straightforward to use an engine that is specifically designed for the 300ZX.