Before you cut and weld, check the position of the hinge bolts measuring down from the top bend of the bedside. It looks like that new stake pocket may be a bit shorter on the very bottom which would throw off your measurements from the bottom. We use that top bend for reference when punching the holes. I don't know if that is a Mar-K stake pocket or not. We usually punch the holes for attaching to the rear sill unless customer specifically requests they be omitted.