S4 seat belts

does anyone know if it is possible to fit inertia reel seat belts to an S4??.
the handbook appears to indicate this is possible but with modification to the mounting bracket on the rear upright

If fitting is possible I know where I can buy the belts themselves but would appreciate info on modification of the mounting point

I’m sure it’s very possible. My Federal Sprint came with inertia belts. Kangol (sp?) is the brand. The take-up box spool box, for lack of a better term, is bolted to the fiberglass that is directly in front of the rear wheel. The belt then come up and out of the carpeted masonite bulkhead as shown, and becomes a three point belt.