[Boater Sam]

Output transformer secondary will be almost zero ohms, if the speaker crackles when you test the primary it must be OK on the secondary and the speaker.
Your quote "can't get a reading" is ambiguous, a short circuit is zero ohms, no reading, an open circuit is high infinitely so no reading again. Better to say a very low ohms or a infinite resistance reading then its clear.

Those resistance readings seem OK, if you suspect the mains transformer has shorted turns I would run it for a time on full power with no loads on the secondaries to see if it overheats.
Sam.