A brake reservoir shouldn't be vented to the atmosphere, since that would let glycol fluid absorb moisture. Is that MC simply the 1980-90's Dodge truck one?
It's not vented. The caps have a bump that kinda makes it looks like they are though, I can see how someone could think that looking at the caps.
Yeah it's the same one as the 90's trucks, plus just about everything else in that year range. They aren't 15/16" from the factory though, Cass sleeves them down (if you request a 15/16" bore) and modifys them to accept the manual push rod without any changes.