Unfortunately I don’t have the tools to drill out the nails, and I have fairly basic diy skills. The metal strips join on the bottom of the amp, so I could carefully lever the nails fixing the metal strip along the bottom upwards, allowing me to lift the metal strip up, which should allow me enough space to slide the mdf panel with tolex out.
But because of the age of the metal it may simply snap or break if I try bending it etc. So I’ve decided to cut out the current tolex covering the speaker, and use extra strong double sided tape to attach some new material on top of the mdf panel. Not an ideal solution, but one which should work!