Youcan order the plates that are threaded and weld to the underside of the floor pan at the major Mustang parts vendors. You would need 4 plates. You can use the rear belts from a 66. You will also need the bottom rear seat from a 66 that has the holes for the two middle belts. You can also get the bolts from any of the parts vendors too. Kentucky Mustang has a moderate parts yard. Ask for Duane. He might have the belts at least. It might be cheaper to buy generic belts as mentioned above. If your concern is passenger safety, then please get the plates at least, don't drill a hole and run a bolt through. You would be amazed how many cars I have seen come through like that. It will not begin to hold a passenger in place.