[morzh]

This transformer is not the best candidate to be a replacement.

For starters the 84 tube in it sits on the same filament voltage which is 6.3V.
However the 5Y4 is a 5V filament tube.

Of course you could replace the tube with a 6.3V rectifier but then you start looking into things like is the tube adequate etc.
Also you have to account for the 6.3V filament winding on the new transformer being capable of the current it requires to run all the tubes now. Plus the pilot lamps.
And of course the rectifier voltage winding itself, you have to make sure it is adequate both in voltage and the ampacity.