David Baker has mentioned this program to me--I think he was listening to it in 1940s Indianapolis, partly because no radio station in Indy at the time was playing anything close to the music that you describe above. (If you're interested, IJA, I wrote a piece about Indpls jazz several years ago in which Baker mentions Randy's Record Shop.)
I went to school with David and have known him since he played trombone (originally) - - and that radio station, WLAC, was, I think, one of those 50,000 watt signals. The music the jock
played was excellent and was wide ranging actually. These 78s were called, unfortunately, race records - -but in my little town the record dept of the local 5 & 10 had a "special" section
with all those artists. Blues, jazz were all mixed in together.