Please excuse my utter ignorance on most things regarding video, but I cannot help wondering: If my math isn't completely off, then the pixel rate of a 405 line video signal is 'only' around 5.5MHz.
With the speed of todays PCs it ought to be possible to simply synthesize the video signal in real time using a program combining brute force, data reuse, double buffering and table lookups. Then the video generation exercise is reduced to finding a way of converting this stream of 5.5 million bytes per second into an analog signal. That might mean convincing a video card into lending us its D/A converter via DMA in some fashion. Maybe another forum member has a better idea of accomplishing this.
Just a thought...
Frank N.