So Mega Man 9 and 10 essentially have "native" PC ports via Mega Man Legacy Collection 2. But something really weird is going on with their resolution, even beyond the forced 16:9 aspect ratio with borders.
I was able to get it down to 224 pixels tall, and you could tell that the vertical scaling "locked" to 1:1, but there was absolutely nothing I could do to get horizontal scaling to lock to 1:1.
The horizontal resolution should be 256. But even with me trying to adjust the horizontal resolution to allow the extra 16:9 space (then essentially cropping out with short timings in ArcadeOSD), it seems there was nothing I could do to get 1:1 on the horizontal axis.
It's been a while since I experimented with this, I just now remembered to post about it. But my best guess from that experience: it needs to be hacked to actually get it to display correctly at 256x224. Hack in what I way? I don't know. There seems to be some kind of intermediate frame buffer being used that does not line up with the game's native 256x224 resolution
I ended up just playing the games in Dolphin, where you can get a 1:1 lock on 256x240 (letterboxed 224p). Only problem being there was likely a small input lag penalty for emulation, which you could probably eliminate by playing the PC versions instead