DIY Solid State Multiplex Adaptor Plans?

[Captainclock]

Hello Everyone, I have a late 1950s early 1960s vintage Magnavox Console stereo which has a mono tuner with provisions for a stereo multiplexer adaptor and I know that the multiplexer adaptors for these things are kind of getting harder to find and when you do find them they usually want over $50+ for them on that auction website and anyways I was wondering if there was some sort of FM Stere Multiplexer kit or plans that one could build one from scratch using solid state components that would just hook into the multiplexer RCA jacks on this Magnavox Console's Tuner to make it capable of doing FM Stereo so that I wouldn't have to sink a ton of money into buying a unit off of that auction site. I would like to eventually see if I could flip this console if you know what I mean, and I would like to see if I can get it so that it can have FM Stereo Capabilities so that it would be more desirable and fetch more money.

Thanks for your help,

Levi