Will a 240sx manual transmission fits into an automatic 240sx?

yes but you will need to swap over these parts. - 5-speed transmission - 5-speed crossmember - 5-speed driveshaft - Flywheel and MT bolts (marked "MT") - Clutch and pressure plate - Release bearing - Master and slave cylinders - Hardlines and rubber line from master to slave cyl. - Clutch pedal - Brake pedal (optional, can cut the automatic break pedal) - Boots and brackets for shifter assembly