And while I'm posting pics.... Anyone have any info about the markings of "F" and "R"?
I have high confidence that the master cylinder I have here is the original one that came from the factory mid-1970. Note that the "F" and "R" circuit markings are STAMPED into the cylinder body, NOT cast in. In fact, if you look close, you can see that there was some sort of grinding that took place before the "F" and "R" were stamped. Like they ground off the original marks and restamped the master with the front and rear as documented on the early cars.
Here's what I'm talking about... If you look closely, you can see the grinding marks and the stamped "F" and "R":