Shoulder restraints for '86 Barracuda

My dad and my son have been rebuilding a 65" Barracuda for my son to use as his first car. He just got his license today and the car should be ready in about two weeks. I would really like to have shoulder restraints installed before he drives it. It has lap belts already though I’m guessing they could use replacement. Any ideas on where I would go to have that done?