I have talked to a couple B17 radio ops from WW II, and one from Britain where some Lancasters had the BC375.  CW was the preferred mode, TX's were set  up on the assigned freqs for the mission, but one problem was what was tuned at sea level, was a different animal at 25,000 feet and -40 degrees.  The Brit radio op said he never used the 375 in his plane other than routine checks and set ups.  The primary reason for the 522 being retrofitted was because the Brits used their version, of which the 522 was an exact copy, and all on FM.  Freq coordination for the Allies was almost a cluster, while the Germans came very prepared in the cross service comm area.  Check out the attached pic of the SCR522, the PE73, and the antenna reel after a fight.

Charlie