Good equipment using a conventional E-I transformer usually uses a copper band around the outside of the core as a screen and it's very effective. If I replace a hot-running E-I transformer with a toroidal one, does any Islander have experience as to the requirement for a screen for this? I can make one or two "panels" to go either side of it with copper, aluminium or steel.

The original transformer, as with many Japanese designs, was made for 60Hz and running at 50Hz really implies it should have a slightly larger core.