Thank you all for the responses. I will work with the following points:

1. Determine if the manual specifies the nature of the VOM/VTVM used to read
voltages. IIRC, many manuals of that era specified 20K ohms/volt meters ---
but some manuals did not specify anything at all.
2. If a resistor starts going bad, it usually increases in resistance. I
did not know this, and it is a very useful bit of information. As mentioned,
if an in-circuit resistor measurement is much higher than the nominal value,
then there is definitely something wrong.
3. Consider pulling tubes to effectively "lift" the ends of some resistors,
making measurements easy.
4. If nothing else works, lift one end of a few resistors.
5. I am over 60 also, and using a glass to inspect the resistors could be
interesting.

Regards,

Bill - W2WO