However, after some thinking I've come to the conclusion that there's no point in continuing.
I don't have any PAL games apart from SM64, and with Everdrive 64 my NTSC N64 will boot anything I'll throw at it.
There's simply no need for stuff this complicated.
I think something based on ATTiny would be much better. After all, all it needs to do is just to read the reset button on power on and switch the clock synthesizer and video encoder to PAL/NTSC accordingly.
Fosstodon is an English speaking Mastodon instance that is open to anyone who is interested in technology; particularly free & open source software.