You don't have to check all that or pull the PCB;

ALL you need do is measure the Heater AC, at those 2 orange leads.
Using the pic from previous page your meter reads 7.8 VAC so to find out what the DC voltage should be After the rectifier you just multiply that number by 1.4
Answer = 10.92VDC (NO LOAD)
IIRC you mentioned it read over 9 volts and climbing over 10VDC with no load. So it's working right,, (just too high a voltage cause some clown fluffed up in the design dept)
It won't be perfect match due to a some loss in the diodes but within a volt so will tell you the rectifier is working.
Under load it will drop a volt or so but obviously not enough to get back to 6.3 VDC
So Insert a 5Watt resistor in series with one of the orange leads, The AC side of Rectifier
Start with 4.7 Ohm and read the DC voltage,, work up or down as needed. saves a whole lot of maths

cause I've forgotten how anyway

When it's close to 7Volts DC,, insert some valves and read the filament voltage again to check you are within the +/- 10% tolerance,
wait for the Valves to heat up to get working voltage.
AX7 filament is around 300mA and EL84 is about 700mA so Total heater current will be around 1Amp.
You can use block connectors to add the 5W resistor and mount the resistor on a chassis then run wires back to PCB.
Oh while you are inside this thing,, cut those cable ties.(we call them zip ties)
Separate the **Mains wires** from the *Secondary wires*.
A common practice but potentially fatal if mains wires melts onto secondary wires.
May never happen but that practice would be an unacceptable safety risk in hospital and military equipment.

Rebundle the 2 sets of wires and re-tie then you know it's safe.
Phil.