Good morning Grigg.
The MC I have is from a 1970s era Jeep CJ and was originally firewall mounted. I'm using it under the floor in the original '36 Chevy location.
I totally agree with you about finding out what the original factory setup was. Unfortunately I'm an example of a an analog person in a digital age. Despite my sons and now my grandkids trying to teach me computer skills very, little sticks.
That's why I was hoping to find someone who's done a conversion like mine who's example I could follow.
Some MCs have residual valves behind the inverted flare seats but the one I have does not.
In theory, at least, a RPV is required where the MC fluid level is below the wheel cylinder fluid level. That is not the case on my '36 although parking on a steep hill could cause that problem.