S14 seatbelts (95-98) work, but you must fabricate or ensure you have the mounting bracket for the main reel, and trim the existing interior panels.
The plastic trim piece behind the door, specific to manual belt cars.
While parts were once cheap, proper manual seat belt kits can now cost upwards of $800 USD, though using S14 belts is more economical. 240Sx Manual Seat Belt Conversion
Resources for these specific automotive components.
14mm shoulder bolts to attach the seatbelts. General Installation Process S14 seatbelts (95-98) work, but you must fabricate
Both driver and passenger front assemblies. Manual Belt Buckles: The floor-mounted buckle/receiver.
After conversion, the seat belt warning light on the dash may stay on for 3-5 minutes before turning off. S14 seatbelts (95-98) work
Install the manual A and B pillar plastic trim pieces.