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Anyone consider replacing R5, R6 and R11, R12 with LED's for bias? Any suggestions?

LED bias can be a good thing, but I suspect there may be some trick in properly matching the LED forward voltage drop to the correct bias voltage for the output tube. There's no guarantee that two different output tubes will bias correctly at the same voltage, either.

I'd also think about whether or not the plate supply needs any kind of regulation if you are going to LED bias. If the line voltage fluctuates, the plate and screen voltages will move around a little, but the LED bias voltage won't.

R11 and R12 should NOT be replaced with LEDs. That is a split load phase splitter and the resistances are carefully calculated to obtain a symmetric output.
Also not all LEDs have the same voltage drop even within a batch of the same kind. I use a test rig with a four AA cell battery holder with various selectable series resistors to actually measure the forward voltage drop. That way I can match the LED to the application.