Sorry for only giving you only a few hours' notice, but I just learned on the website of Toronto's CFZM radio that tonight (December 11th) at 10:30 P.M. Eastern Standard Time, they will (as part of their weeknight rebroadcasts of old-time radio shows) rebroadcast a 1944 episode of "The Jack Benny Program" with a young Frank Sinatra as the guest star.
(This is part of CFZM's salute to Frank Sinatra on the 100th anniversary of his birth, which is tomorrow, December 12th)
According to the station's website, this episode was first broadcast in 1944 and it titled "Jack Offers Frank Sinatra Dennis Day's Job". I would think this was during the time that Dennis was in the service and Larry Stevens was filling-in for Dennis.
CFZM is a 50,000-watt station that at night should be heard across most of the Eastern portions of the United States and Canada; beyond this area, you can go to http://www.zoomerradio.ca , click-on the "Listen Live" icon at 10:30 P.M. Eastern time, and enjoy!
By the way, CFZM will likely be rebroadcasting classic Christmas radio shows the next two weeks (December 14th-18th and December 21st-24th), and I suspect there will be at least a couple of Jack Benny shows (if not a full week of Jack).
Usual disclaimer: I don't work for CFZM nor know anyone who does. But I found out this information and wanted to spread it to Jack's fans.