Musicaire or Aircastle?
 

Saw this on ebay in antiques, not the usual category I check.

http://www.ebay.com/itm/Vintage-1940...item19cf1c4b14

Here is my unrestored Air Castle (Spiegel?) FP604 and its schematic.
Attachment 173819Attachment 173820
As can be seen from the schematic, unlike the Musicaire, mine is a battery "farm set":saywhat:. Found at an antique store 35 yrs ago near Altoona in a very rural part of PA.

Now for the question; How many different versions were made
of this set and who really made it?

Don't know how many versions exist, but you have a nice set that should finish up well. It could be converted to AC with a power supply built in.

Have this to say about the one on ePay: That looks like plywood that had a quick coat of ordinary varnish on it. That's not worth $300, more like $30.