Two years ago I started a romhack like that, but never continued. Mainly because I wasn't absolutely sure that I got the hitboxes right. But when you play it, it seems they are right.
I did simple adjustments of the sprites to display the hitboxes. I do not remember hitboxes that were bigger than the sprite boundaries, but I might be mistaken. And, sock master, maybe you can explain what you mean by hitbox ranges not being constant.
I created two prototype versions. The first one only displays the hitboxes. The other one displays the hitboxes and the outline of the original sprite. I will provide both versions in the next messages.
[The top displays DUEL, because I took a template versioon of that romhack as basis for this one]