[OZ4]

Ted
It should be easy to check if it's been rewired by checking where the filament pins are wired. 
According to my book filament pins are:
5U4 has them on pins 2-8
5X4 has them on pins 7-8
The wrong tube shouldn't hurt anything here it just won't light up.
Just check with the tube out (no power), there should be pretty low ohms readings when you find the right ones. Remember these are only 5volt windings. But watch out if you power it up and check voltages there will be very high voltage too!