Early A shoulder belts?

I agree that vintage cars are dangerous but guys like us still love driving them and will continue driving them until we are put underground. Had we been in the Barracuda we would probably be in the morgue. I sincerely thank Chrysler for building a very solid car.
I watched a video on installing 3 point belts in a early Mustang, which are built much like our Barracudas. The upper mount was welded to the reinforced coat hanger location. Neither of these cars have the structural strength for 3 point belts. However, anything is better than nothing. Though this method isn't the greatest it gives more restraint than a lap belt thus making our cars a little safer than stock. My car has no reinforced floor belt locations so I will need to reinforce the mount locations with large plates and follow the example of the Mustang for the upper belt mount.
I like your plan to make things safer!
I did the reinforcing plate on my '37 Pontiac streetrod. 3/8" plate with a 1/2" nut welded behind it is pretty secure, though that car has considerably heavier steel than my Valiant! Mine's a convertible so I like the Sebring seat idea.