Once you get it all up an running you may wish to consider modification. The phase splitter design is err.. sub-optimal is the kindest expression which comes to mind.
Just look at the values of the 2 anode load resistors.
Those "cheap" motorised pots (volume control) don't have great tracking between the 2 gangs. Silicon Chip used these for their 5000 Series preamp too. I substituted the ALPS motorised pots in the 3 preamps I have built. They are physically larger. You would need to check if they can be fitted. The preamp boards had alternate mounting holes to accommodate the ALPS pots.
Cheers,
Ian