Drewmac,
The reason I am going with the route I am going is the anchor point in the roof is solid and a proven attaching point with a lot of surface area forward and aft of the anchor point to absorb pulling force on impact which is why Chrysler used it in 1968/1969. I have a 69 notchback and a 67 notchback. No structural changes were made in this area except the addition of the anchor point about where the coat hook hole is on the 67.
Attaching the upper anchor point at the top of the quarter panel edge inner structure like that is a serious weak point. Theres not enough metal forward of the anchor point to absorb the load on an impact. None of us wants to think about the unthinkable, however when putting these things in your car, you have to think about the unthinkable. During a violent front or rear end collision. Depending on the impact speed, your body weight against an anchor point can triple your weight in force. Ex. a 225 lb man can exert 675 lbs on those anchor points on impact.
You can buy those vert shoulder belts and put them in a hardtop, but every belt manufacturer has some lawyerese speak about how they arent responsible for the installation and use of them. Probably because of the non stock unproven anchor points. If they fail from a substandard mounting point and you eat the steering wheel they arent responsible. Plus they will interfere with the rear window cranks.
