10mm x 3/16 line I think it an AC Delco it does have a semi flat round gray metal booster about 10 inch in diameter and 6 inch width
I think this is it, https://www.ebay.com/itm/BRAND-NEW-...wA3dYlMLt&fits=Year:1986|Make:Mazda|Model:323
I agree with Henry. Mazda used a magnetic sensor that slid into the mouse hole at lower center of the plastic reservoir, there should be a float with a small magnet inside the reservoir.
Looks like the MC that was on the 90-94 Protege/******/Laser but the MC looks to be Fe rather than Al. Definitely a Ford/Mazda piece... 1985 626 2.0 MC? D'oH! Missed Henry's post.
We've got a B2200, a Protege and an ****** in the extended family fleet, and they all have the angled reservoir. The MC in question is interesting in that it has a horizontal reservoir, so is suitable for a car where the MC is level as opposed to angled slightly upwards. I would stay away from these modern master cylinders for old cars due to the metric threads, plus the plastic looks ugly. Surprisingly, they still have inch size bores.