Scratchy pots can also indicate the presence of DC in your audio which could point to a failed input coupling capacitor.

In your case there will only be one wire going to each side since you don't have a split secondary.

One red wire to each side. Black for the center tap.  And you can tape up the extra secondary wires and leave them disconnected.

I think the - lead on your speaker could be switched to connect to one side of R8 or the other for "tube fusion on" or "tube fusion off." That's probably what you mean by "short over" the 470m resistor.

I've got an old 70's solid state amp that needs some reworking so I will try your schematic above for the power section.  Thanks. Let me know how it works out.