The spacing of the 6L6 tubes is odd.
The tube rectifier is where it belongs, on the far side.
But the plate that covers the unused socket hole definitely looks Fender.
The four hole spacing may have been for a four tube amp without the tube rectifier.
Who knows what went on at the factory?
They may have came up short on the correct chassis & used a different one.
I do not know that Fender used voltage selectors.
It is most probably the 'ground polarity' switch that is missing.