Has anyone solved the transition from the original 2 point lap sash seatbelt to installing a 3 point inertia reel seatbelt in a 240z?

Yes.

I have the OE belts in mine but if wanted something better I'd google "240z seatbelt upgrade classiczcars.com"

I also have the original 3! point belt in the 240z and also a 4 point rally safety harnas on the original bolts and on one of the top of the rear strut towerbolts.

I always use the harnas, the old belts are under the seats. (the third belt just hangs in the rear on the side of the roof.)

@steveJ , was very funny to just say: Yes !!  

Seatbeltplanet is my goto. 

https://www.seatbeltplanet.com/i-30499407-1970-1973-datsun-240z-driver-passenger-seat-belt-kit.html?q=

I get them to add a 9” drop strap from the shoulder belt hanging point to bring it down closer to your shoulder.

Quite a challenge on an early car with the tool storage bin covers thingys behind the seats. Modifications required to properly mount the retractor flat against the luggage riser. I use a drain hole to bolt an angle bracket down. Requires you to build a bit of a crush tube in the frame rail so you tighten that long bolt down….. 

This is the Roadster Retractable 3-point belt from Wesco, a very comfortable belt.

The retractor is mounted at the original shoulder belt location using the OE bolts.

The lap belt also uses the OE bolts and locations.

Here is the website and belt details. If you order, specify the 11" rigid sleeve.

https://www.wescoperformance.com/noname.html

Edited April 9, 2024Apr 9 by jfa.series1