RGB Mod to TV with only coaxial?

[izlude]

Hi all. My first post, so here's a few details. I've RGB modded before, but only with the use of a tutorial on specific models. I have no knowledge of analog tech, just follow the steps and it's done. So I may come back in the future asking about TVs that have unfamiliar landscapes etc

OK I found schematics for my 19PR15 C122, a Coaxial only Magnavox TV. Datasheets all show the necessary bits like R G B input pins and Blkin, heck I could even add composite if I wanted... except I just realized there's no way to access AV1 via the computer, perhaps it doesn't exist on this set? Normally I could use the sync with the composite input (and I could definitely add my own composite input thorugh the CVBS & ground right?) but again, no way to switch over to that signal... or is there a way?

If all else fails, is there a pin that I can use directly on the Jungle IC, seeing as being on Channel 3, you're still able to access the menu and I just wire up to that pin and make it a "ext sync".