I own some of the Radio Spirit disks, and have recently stumbled upon the Superman podcast which has several episodes available (http://feeds.feedburner.com/Superman
). These episodes start out with the announcer saying "Presenting the transcription feature... Superman." What does 'transcription feature' mean? The voice of Superman/Clark Kent does not sound like Bud Collyer. Granted this could be due to the varying qualities of the mp3 used for the podcast. There are also no mention of any sponsors. Where the Superman scripts ever given to actors in other markets to perform?
A transcription feature means the show was not broadcast live, but rather recorded on an electrical transcription - essentially a 16 inch record. This is because Superman at that time was a syndicated series which meant the show was recorded, put onto discs or ET's and shipped to participating radio stations. Superman was not a network program until later.
You don't mention the web site, but I suspect you are speaking of http://www.supermanhomepage.com
which has a copy similar to what you describe. It is Bud Collyer, but remember he played both Kent AND Superman by raising his voice when he played Kent. The copy I listened to at the web site was a bit higher pitched, which may explain why it doesn't sound like Collyer. Even if it wasn't that web site, that is most likely the explanation. Collyer was always Superman and Kent from start to finish on U.S. Radio.