I'm in the process of putting my 63 together and am considering retractable belts too. I need to find a way to reinforce the rear of the cab to mount the shoulder belt too. There's nothing but sheet metal back there and if the belts ever were needed to do as they were intended, they would just pull right out of the cab. I am thinking that I need to cut a slit into the rear cab wall, slide in some 1/4 inch flat plate (curved to match the cab), tack weld it in place and weld the slit shut. I just haven't got that far yet,
Scott