[Arran]

Terry;
  If it has the metal plate and a phono jack it may be a Canadian model, which would not be all that odd to find in Michigan since it border's Ontario on both the Southern and Northern peninsula. I think that it may be a 39-340, but I'm not sure, some Canadian Philcos didn't use the date code prefix, especially in the 1940s. It also is not quite true that they are free of rubber wire, free of rubber covers hookup wire in the point to point wiring, but they still had some in the IF cans, and maybe in the transformer leads on the 1939 models, even so it's still an improvement over all rubber wire.
Regards
Arran