[Vanne]

that would all depend on what you have inside your car?

if you have a rollcage, the shoulder straps wrap around the rear STB. The Seat mounts should have anchors for the lap belt and the center (between) the legs either go through the bottom of the floor pan, or onto a sub section made for the seat mount.

There are lots of varying versions of this. just pay attention to the angle of the shoulder belts.

If you have no cage, then there are other ways guys have done it.