Is there a medium-res to NTSC convertor?

I'm trying to fix a standard Terraburst arcade machine that was discarded because the giant medium-res CRT monitor died. I'm trying to see if I can convert the signal to use a TV instead. I believe the deluxe used a 50" projection TV (the remote in the manual has a Mitsubishi logo on it), but can't find info on how that is wired or works. I'm assuming there's an extra video convertor board.

Every encoder board I've found explicitly states that it DOESN'T work with medium-res. Is there a good solution to make this work?

I can even build a board if I can find a good schematic.

By medium res you are referring to 24khz right? if that's the case there are LCD TVs and computer monitors that can handle that signal, I use a cheap Samsung 21" tft for my model 3 and model 2 boards every time I can't be bothered to swap resolution mode on my dual res arcade monitors.

The Micomsoft XPC-4 will do it, though that's a pricey option.

I don't think you can input composite sync with the XPC-4 its for PCs which all use H/V sync

With my XPC4, I used composite sync for 15KHz RGB sources, including MVS. I'd expect that will work for 24KHz and 31KHz sources too.