NOS genuine Kangol 3 Point Seat Belt complete set for one seat. It is 5 band on the long belt and 4 bands on the latch with the Kangol sticker.

These have a 309 part number because they are longer belts than the ones for the W108, 109+ 111, but you can certainly adjust the long strap or have it cut and restitched. The only other difference is it’s a 5 band strap whereas the others are 4 bands.
You can then also change the Kangol sticker to the one with the Mercedes star which are available online.

If you are restoring a six figure 6.3 or 3.5 coupe or cabriolet where in the world do you think you will find another. You may find reproductions that are not correctly zinc plated on the hardware and of course the strapping is changed.
All 3 that I have are 1971 dated on the label.

Ask about individual parts like the caps, All Star spring retractors- NOS and used, and used belts and parts that I have.