Thanks for the comments. I agree that it's got some signs of a quality frame, and the paint is actually better than it looks in the photos (at least it's not a rattle can job.) There is a lengthy serial number (9 or 10 characters,) which does suggest a large production shop. I don't think there's any connection to the newer Masis, this one has details that look 80's-ish to me, and it's not nearly as nice as an earlier Masi.

Coincidentally, I spotted a low-end Raul Mesa MTB at a local shop a few months ago, and I took a photo of the only branding on it to research it later. I never got around to doing that, and I only remembered it this afternoon