In the photo's so far, the neutral of the mains lead appears to be connected to the chassis but I can't see any isolation between the chassis and the metal case.
That aside, so far as I can make out there are two series heater circuits one for the scale bulbs, UCH42 and UAF42 and another one for the UL41's, UY41's and the other UAF42....Auto transformer with two taps...?
Definitely paralleled UL41's so far as I can see, common 75 ohm cathode resistor, common 680k grid return resistor, individual 2.2k grid stoppers, looking at the wiring and the output transformer suggests the output transformer might be of the hum cancelling type, the 1st AF (on radio) uses grid current bias, the grid resistor is 22meg, the anode is fed from a decoupled supply (100k and a big wax TCC at least) the anode load is 220k, the screen feed is via a 3meg.
The surge limiters for the rectifiers are 180 ohm fed from the mains via the on/off switch, there's a switched mains outlet socket on the rear of the chassis.
Lawrence.