[Arran]

Fred;
  I looked up the 6F7M and the 6P7G, the tubes are identical electrically other then the pinout, same voltage and current ratings, same amplification factors, same transconductance. I think that like many tubes decided to make a spray shield version of a standard RMA tube type such as the 6F7 by coming out with the 6F7S. When octal based tubes hit the market in 1935-36 they decided to manufacture an octal version of the 6F7S and called it a 6F7M whereas when either RCA or Sylvania decided to make an octal version of a 6F7 they called it a 6P7 or a 6P7G but used a different pinout. The reason I looked into this is that I just acquired a Rogers set that happens to use a 6F7M, but unlike your Deforest-Crosley someone has replaced most of the spray shield tubes with metal ones, and I have not investigated if they replaced the 6F7M tubes with something else or how they did so.
Regards
Arran

P.S What model is your Deforest-Crosley? There should be a name stamped or stenciled somewhere in the back of the cabinet. Also what's the chassis model number? It should be something like 7DXXX.