Originally Posted by Richard@M-World
Yup as Kevin says some racing seat mounts offer attachment for the OEM seat belt receptacle. You can utilize the factory 3-pt system this way.
As for a 6-pt system, the only safe and proper way of installing them is to attach the shoulder belts to the roll cage/roll bar, and the anti-sub and lap straps to the chassis of the car with proper, welded reinforcement plates. Don't let anyone convince you otherwise.
Here are some pictures from the GT4 as they came from BMW. Courtesy of CheckCaptain.
Left lap strap (left side of seat)
Right lap strap (right side of seat)
Anti-sub straps (under the seat)
Great info thanks which floor mounts would fit this need. I it matters I am looking at OMP and recaro seats.
2011 E92 M3 Coupe Jet Black ZCP: Piper Cross Filter, AA Race X-Pipe, BW Race, CF Spoiler, and GT4 Front Splitter, APR GT-250, Stoptech ST-60, MCS 2 Ways, Apex ARC-8, Sparco Ergo Seats, Alekshop: Cage, Subframe and Diff mounts, Oil Cooler, CSF Radiator and Power Steering Cooler