Madbean was right. A 1590BB will actually fit. I still think it would be pretty hard to have multiple burn runs to make art big enough to fill the whole enclosure, but I'm sure it can be done if someone is suitably motivated. I am not.

The powdercoat on this one was a LOT thinner, so the final cleanout was harder. My pick kept jumping out of the groove and scratching the surface of the non-etched areas.
Also, I noticed that when the laser software is in "preview" mode (where it shows a rectangular outline of where the art will be etched), it leaks a bit of power and actually very lightly marks the powdercoat. You can't see it unless you hold it at the right angle, but it's annoying nonetheless. I think a piece of paper over the enclosure during preview will fix this, but it's another silly step.
Anyway, this little thing is still impressive to me despite the various shortcomings. And frankly, for my own personal builds, the output I'm getting is pretty well "good enough for DIY". I'd like a little bit more improvement, but it's close.