I bought 3 point belts for my 1966 C10 from Chevy Duty. I welded in brackets on my B pillar for the upper mount. They work pretty well. The only thing that I want to modify is that the short part of the belt is just a little two short, meaning it barely pokes through my bench seat, but it's doable. I hope to make a short extension to give make buckling it a little easier.
Fit and finish wise they look identical to the lap belts I removed, nice shiny all metal latches.