Rear seat belts

[samuel smith]

I'm putting rear seat belts in my 641/2 Mustang coupe. There are
six existing holes in my trunk right behind back seat around center they are not being used what are they? Can I use two of these holes to attach the female seat belts and drill another hole on the right for the Male belt (the left already has a pretty large hole I can use)? Or, where is the best place to drill the four holes?

 

[zookeeper]

Your original seatbelt holes are easy to find, since they would have a backing plate under the floorpan. Crawl under the car and you should find four oval or rectangular plates, already tapped for bolts, spot-welded to the floor pan. Two will be in the center and two will be a bit farther out on each side.