I'm looking at the schematic for this, and here's what I'd like to see done:
Say farewell to A5 and A7, and all associated components.
Replace it with a unity-gain single-ended discrete FET/bipolar stage powered from the +47vdc rail
Say farewell to R58 and R73. Replace with 330 ohm and 47 ohm 1 watt resistors configured as a divider. Or, replace U1 and U2 with 7805 and 7905 (that's probably easier)
Say farewell to the 12AX7 tube. Replace with a 6GM8 tube
Turn R62 and R98 into a voltage divider by adding a 25K resistor
Say farewell to A2 and A10 and associated components.
Replace with a dicrete bipolar push-pull stage powered from the 47vdc rail as well, and an output transformer.
So essentially, you'd get rid of the starved plate tube (since the 6GM8 will run properly on 35vdc, and it's a 9-pin octal like the 12AX7), you'd increase the headroom of the solid state portions, and you'd be adding an output trafo.
I've got one of these coming to me in a week or so. I think I'll do it. If anyone is interested, I'll post the results.