[MrFixr55]

They may be either a factory mod or a documented post manufacture mod.  Often, this info does not make it into third party service info such as Breitman's, Riders or even Sams, whether or not the documents were published in cooperation with the manufacturer. 

In older radios, the use of "voltage dividers" to supply a predictable screen voltage that does not vary based on varying current was common.  I looked at the 920, 921 and 922 and can't find the resistors.  My guess is to measure the voltage for the screens.  If accurate and non-variable, then you are good to go.  if the resistors are out of spec based on their markings, replace them.  I used a 100V drop across the resistor, instead of the approximately 80V in calculating power dissipation which works out to be about 1/2 Watts.  1 watt resistors should be OK, 2W better.  Use carbon or metal film.  Since these are DC voltages that are likely bypassed by a cap, RF should not be an issue but do pay close attention to replacement.  Hopefully, you don't have to change them, as they look quite buried.