When I did the interior of my '56, I used a 60-40 center seat from a '99 Tahoe that was tight against my cab corners so 3-pt. belts were not an option. I converted the 3-pt. shoulder belts to lap belts by cutting the retractor belts and having the belt ends resewn. That way I didn't trash out the interior with loose belts lying on the seats. The retractors were mounted to the floor in the cab corners at the rear of the seats. Note that the retractors you use may act weird and lock up if not oriented straight up-and-down as you work with them. The button-end of the belts in my truck were attached to the seat but on original seats that end would have to be mounted to the floor and brought up through the crack. Just an idea.
