I finally got my video capture and editing software setup on my new PC and captured footage of Art of Fighting off of real hardware, in order to finally narrow down what resolution changes actually occur during the zoom effect.
I tried matching up screenshots in Mednafen and Magic Engine in the past, but they appear to not emulate the actual resolution changes and instead literally scale the image to fit the same 256 x 224 window. This only produces distorted graphics outside of the fully zoomed in perspective.
I had wanted to recreate the zoom effect using emulated screenshots, but the fully zoomed out view actually reveals more of the background than is possible to see in the non-distorted perspective on emulators. The horizontal resolution changes reveal more of the background above the fully zoomed in (256 x 224) perspective and less of the floor is visible in Magic Engine. Jumping in this resolution doesn't reveal enough above of the background that is visible while zooming out.
Here is what the changes in play area window visible pixels are:
Zooming in: 304 x 240 to 304 x 232 to 304 x 224 to 256 x 224
Zooming in: 256 x 224 to 304 x 224 to 304 x 232 to 304 x 240
I didn't simply call these measurements "resolutions", as the wider horizontal views add a bit of letterboxing. Those measurements are of the visible pixels in the play area window. It's possible that my framemeister doesn't display the resolution cycling correctly. I can't compare it to what appears on my CRT tonight, but will do so another day.
I had expected multiple jumps in horizontal resolution and perhaps individual frames to jump both vertically and horizontally. I was surprised by the big horizontal jump.
Each resolution change occurs every other frame, so it's "30fps" zooming for a split second.