I'd compare B+ to schematic. If there is less than a 20% increase the droppers won't make an appreciable difference in longevity or performance. I skipped droppers in my TS-4 Moto too.
If you still decide that you need to add a dropper take that B+ measurement and figure how many volts you need to shave off, measure the B+ current off the highest rail past the rectifiers and before the divider resistors for the lower B+ rails (the best place to put such a resistor). Use ohm's law (R=E/I) to calculate the resistance and multiply voltage and current to get your wattage (P=IE ...Mmm pie
) rating (it is wise to ~double that number so your new dropper resistor is not too hot to touch in operation).