Question on how to modify an old TV with AV inputs

[Aussie Bloke]

Hi all. I have a technical question.

I've got a late 1970s Princess (Australian brand) colour TV with only a VHF tuner and a 1990s portable B&W Radio Shack Portavision TV set and I want to modify them by fitting AV input sockets to them so I can directly input video to them.

However I'm not very certain on how to go about it as my technical skills are a bit limited. My wild guess is running them off the audio and video outputs of the tuner module, is that correct?

Anyways if anyone can give me directions I'd most appreciate it.

Cheers
Troy