Hi Alan,
the pre-war traction had brackets welded to the wing. The mud flap had a flat plate riveted to the rubber flap and this was bolted across the two brackets on the wing. I was fortunate to still have the originals, but were in very poor condition, so I found a roll of rubber from an old conveyor belt and cut the mud flaps from that and fabricated the flat plate from a 2mm steel. The brackets on the wing were very thin and weak, so when I had the wings repaired, we made up some new brackets and spot welded them on. The wings were rebuilt some 20 odd years ago and the brackets and flaps are still in good order.