They are removed because the whole Opamp buffer stage is removed and its just the plate of the 6922 driving the output.
You will need to check the B+ voltage top of both the plate resistors likely modded to Mills 5W wirewounds around that tube. I recall the B+ is supposed to be 240V and the plate voltage is supposed to be around 70V.
If the regulator zeners on the right hand side of the board are blown the 240V wont be clean and it will be quite a bit higher and you will get hum.
If you are in the SF Bay Area I can help you take a look.