300B PSE clone

[Stephen C]

I am looking for parts to build a pair of WAD 300B PSE amplifiers.
I would welcome any advice or first-hand comments on these amplifiers.
I am looking for a source of suitable single-ended output transformers in the UK.
I have a couple of questions concerning the heater supply for the 300B valves

1. The original design has separate 5V windings for the two output valves. Should these be wired in-phase for minimising hum, or out-of-phase?
2. What is the reasoning behind having hum bucking only on one of the 300B heaters, as these are supplied from separate transformer secondary windings?