I definitely could have planned out this answer better about what master cylinder I have. It's not pictured in Hall's catalog, Precision ProFormance, it looks kind of like PIM's, it has some close looking counterparts in JEGS and Summit, but I can't find what it is.
What I made a mistake on is that it does have an adapter. The adapter is also machined aluminum, 3/4" or 20 mm thick. It has two side bolts on the m/c. It's machinded aluminum with numbers stamped on one side.
It looks like a bunch of selection for you, but it'll be a surprise if you get the exact same master cylinder I have. 10 to 15% chance at best. Probably you have ideas already, so maybe this helped, maybe not.
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