Reviving an old full wave rectifying valve

[Kalee20]

Transformer Windings don't like being left floating so it's best to give them a bit of Load.

That can be true of an audio output transformer in a valve amp. Audio transients can excite self resonances to give excessive voltages. These can damage the valve and/or the transformer.

Not true for a mains transformer which is handling a steady sine wave.

Absolutely - a mains transformer operating with a constant voltage won't mind having its windings unloaded. In fact it will like it as it will run slightly cooler.

Being it's less loaded as a whole, it is barely possible that the voltages from the other windings may be slightly higher, maybe 1%. But that won't matter.