[morzh]

I dunno what it should be Ohms-wise.
If you know the Ohms for the 43 then

Find out from the paper what C voltage shpuld be (use the output tubes plate voltage if not directly shown).

Then add 43 ohms (R43 in Ohms) and 3.4Kohm from your field coil.
Then find out total power:

Ptotal=(C-square volts)/(R43+3400).
Then the power dissipated by R43 is

Ptotal*R43/(R43+3400).

Now use 2-3 times that power for rating of the res 43.