How to Upscale OTR Files to Stereo?

[Saylien Brown]

Hello,

I've been noticing on a certain OTR station (20thCenturyOTR) that a 
lot of the OTR shows they play seem to be in a stereo format. Mainly 
the detective shows (Johnny Dollar, NightBeat, etc.) They really 
sound damn good. No pops, clicks or anything. It's like the shows 
were recorded in the late 20th century, not the mid-early years.

Does anyone know how they accomplished this? I mean most if not all 
OTR shows from the 30s, 40s, 50s... have been recorded in mono format.

Please share the software used and any additional plug-ins I would 
need to upscale some of my favorite OTR shows to stereo (For my own 
listening pleasure of course.)

Thanks.