I was surprised at the pic Harms posted, then today, I checked the gap on my car, same thing, fingers easily inserted. Also worth mentioning is the radius of the door corner (behing scotts arthritic middle finger knuckle ;)) is much smaller than the radius of the rocker. It's almost as though the rocker forming dies were not designed with the door frame and skin available. Either that, or extra clearance for body twist in high hp cars?
These cars were designed by hand on drafting boards. It is actually amazing that the parts fit together as well as they do. The engineers had absolutely no way to build computer models back in the 60's. The best they could do was print blueprints on vellum and lay them on top of each other to see the parts mated up.
