Thanks for the suggestion, but I am a ZX Spectrum zealot. The spectrum had practically no shielding at all. In any case, I am not going to gut my Speccy, and if I had a Commodore 64 I'd probably leave it alone as well smile
I bet that the casing from old PC PSU's will do just as well, though it probably is a lower grade of mild steel. However with this latest design hysteresis is a non-issue, so annealing shouldn't be needed anyway.