Skipping forward a bit.
We got the boards cloned onto modern FR4, with the inclusion of a solder resist mask. They are a true mirror image pair for each channel.
Some of the resistors have been specified much higher in terms of power rating compared to the originals - they run hot, specifically in the phase splitter circuitry. I believe the original resistors were 2W rated, whereas now I used 7W vitreous enamel wire-wound types instead. All non-electrolytic capacitors are polypropylene types. All resistors are metal film aside from aforementioned wire wound types.
Perhaps shockingly the smallest resistors in the picture are actually 1W rated, despite looking like 1/4w or 1/2w types. They are minuscule for their supposed power rating but they are used where 1/4W resistors were specified and aren't dissipating any power. I would struggle to treat these as true 1W resistors, they are so small!
All values are as originals - except for one exception in order to run the output valves a bit cooler. The original configuration runs the output valves right on the edge of their dissipation limits. This addresses this.