[Mondial]

Is it possible that the transformer has been replaced? Maybe someone restuffed a replacement into the original sheet metal cover?

Its pretty strange for a transformer winding to increase in value rather than open completely. The original transformer is somewhat unusual in that it has a step down ratio and two independent secondaries. That's why I am thinking that it has been replaced with a more common  step up interstage transformer. The dual secondaries are needed for the negative feedback networks connected from each plate of the 6L6's . If the present transformer is actually bad, you may have a hard time finding a suitable replacement, and might have to use a normal plate to P-P grid interstage transformer. In this case, you would have to eliminate the negative feedback networks (parts 98,99 and 103,104)