I did the swap, the 5E3 is OUT of the Sunn combo, and the Cygnus 5 watt lead head is in it. Sounds grand.
So I went back to working on the 5E3, which is now in a head chassis.
I had to change power transformers.
So, it has multiple primaries, with 120V or 125V as two of the many options.
I'm thinking 125, but what do I know?
Which should I use?