Looks awesome. But i have some ideas on how to improve. :)
1) add the rng fix, to make the enemies behave correct to FDS original.
2) replace the music/sound routine with the FDS one, to reduce lag when screw attacking. This will make the game perform faster. there's no need to use precious CPU on the screw attack sound effect when its' being replaced by a sample. (has this effectively been done already?)