The fenders on my 1939 9N were pretty bad. I had my FIL use a MIG welder and weld the splits and I welded a patch in place over the big hole:
I have a set of skins I pulled off Rustbucket, my 1954 NAA I refirbished, that look a lot like your set. I removed the supports and there was rust through everywhere. Just because I really enjoy trying to repair what most will throw away, me and my FIL spent two weekends welding, grinding, welding again, grinding again, repeat - but had very limited results. The metal is just too thin and burns through, and when you grind the welds down flush it is too thin. We finally threw in the towel and decided if we wanted to repair it we would have to weld patches in place like the pic above.
I would say save yourself the heartache and try to find replacements on those.