A lot of the 3 point seat belts have an anchor point for the retract mechanism mounted at the floor or near the rocker panel. Then the belt goes up to the upper mount and a second lower bracket is often attached to either the rear of the seat track or the seat base, or has another mounting hole in the floor near the rear of the seat base. The buckle end will often share its mounting hole with one end or the other end of the center lap belt, depending on which 3 point belt your looking at.

The few I have seen that mount both the seat retracter and the the other lower belt attachment with the same bolt have different seat belt mounting ends so there is a spacing between the two parts of the belts.

When I install 3 point belts in something that did not originally have 3 point (or any) belts, I always use separate mounting points for the lower mounting points. I figure it spreads the load out more, and makes it easier to grab the belt to use it. I have mounted a lot of seat belts where there were not any. Gene