It almost looks custom. Doesn't match the coloring of the actual dash. If it wasn't, you would think that LMR, AM or CJPP would have it. My guess its custom. Another indicition is the gauge isn't aligned perfectly in the middle, its more to the right. Also the top left corner looks like it was trimmed down to fit in. Just my thoughts. Its interesting to say the least, and doesn't look like it would be hard to mock up, if it is custom, or you wanted to do something like that yourself.
Looks like its just the dash part that surrounds the speedo/tach cluster on 87-93 cars that someone pulled the hazard/rear defroster swtich out and mounted a gauge. You could propably get one at a junk yard and if needed remount the guage. Its custom but not that much.