Help with 1953 single sided front brake plate

[nvmat1]

Hello everyone. I have a front wheel for a Matchless G2CS, which, I understand has the same alloy brake plate as the 1953 singles and twins. The wheel has lots of corrosion and someone has had an attempt as dismatling it. One initial problem I have is with the brake anchor bar - I have the anchor bar with the bolt welded to an alloy threaded insert that screws into the brake plate. The threads on this insert are damaged, obviously where someone has tried to seperate the two. Thankfully the threads in the brake plate are fine. Where can I get a replacement? I assume this may have been a design feature to prevent the anchor bar bolts damaging the alloy brake plate? Any help appreciated. Thanks. Paul