I think Laser cutting these should be straightforward - didn't realise it was the whole thing thought it might have been an adaptor to fit on the existing metal bracket.
Thanks for the detailed help and guidance. I’ve ordered all the stuff I needed thanks to your advice. Just waiting for it to arrive then get it installed and tested.
I have those same speakers and they have perished all the way around. I need replacements too. Did you find a replacement or alternative? If so what did you use?