Finally got Pixel's approval and the source code. It looks doable, but at ~50000 lines of code it's a little daunting.
This is the preview version that I sent to Pixel, so it's mostly guesswork and buggy and certainly feels different from the original. Playable up to the first boss fight. Dual-language English and Japanese :) Tested on 3.10, should work unmodified with most custom firmware.
Will try to do this in four stages:
1. get the windows version working with the alternate screen size (480x272)
2. port filesystem+graphics+input handling
3. port sound+music
4. add menus (key config) etc.
I expect this will take a while, so I guess I'll try my best.