Did this recently for my CoCo 2. Used a mashup of several composite mods floating around (including this one) and built it on a piece of stripboard that fit in the same footprint as the RF modulator. Sourcing the MC1372 was tricky, but NTE makes a replacement, NTE855. I used a 3.5mm TRS jack for the audio/video output so I didn’t have to drill a second hole in the case, and then all you need is a cheap 3.5mm stereo to RCA cable.
Wish I had a schematic but I kinda just wired it freehand.
Looking at the monitor circuit with the two transistors, it's odd how the emitter is just connected to ground through only 122 ohms. Why would you have that 100 ohm resistor there?
Indeed, I found other versions of the circuit which don't have that: