its mainly switched by the 1 and only transistor on the IIc, might be easier to deal with

and yea I have not seen a computer monitor in a long time that will accept ntsc rgb, I have one but its a rgb monitor that happens to accept ttl and vga also heh but its a thousand years old (like first model nec multisync)

unfortunately the active video time is just too long, at 31.7 us, 31.7us is also a vga line but that includes the active video (~25us) and porches and sync

so while it might be easy to overlay the signal on vga timing its going to be cut off on both ends (bummer)