On "When Radio Was" I found the answer to a question that had never occurred to me: Did Barney Rubble (Mel Blanc) ever appear on radio with Fred Flintstone (Alan Reed)?
You may know other examples (In Jack Benny/Fred Allen crossover appearances perhaps) but the one I'm talking about is the Family Theater adaptation (loose) of "Pinocchio" from the early 1950s. Mel is the title character and Alan Reed is the The Lame Fox, whose pal The Blind Cat inspires a cry of "I tawt I taw a puddy tat!" from Pinocchio.