Put an ad in the parts wanted. A lot of people on Fordbarn have redone various vehicles and replaced headlights damaged beyond repair that could be used for donors for your application. The mounting bolts for the 38/9 pickups are the same, they are the same as 35 passenger car, and they are the same as 35-37 pickups, trucks, and panels. I would think the 40/41 truck buckets would be the same mounting bolt since the seal beam bucket is dimensionally the same as the 38/9 pickups. It may be easier to replace the buckets than finding mounting bolts and changing them out.