[Arran]

Try looking on the AES website under guitar amp power transformers, more of those are horizontal mounted then the standard Hammond fare, they also seem to be cheaper (volume sales I guess?) Most power transformers for radios had a 350-0-350 volt H.V secondary, and a 2 amp 5 volt winding for the rectifier tube, to figure out what the 6.3 volt heater winding needs add up the current draw of the tubes in the set, most are 300 ma each, plus whatever the audio output tube draws 800 ma to 1.2 amps depending on type.
Regards
Arran