This one? BTW, Brad, I hope you don't mind me posting this....Things may have changed, but those rotors were not OEM spec to 67-69 B body bendix. They did not work. 70 was different from earlier so a 66-70 is not accurate.
We were talking pre 70 B body Disc brakes. B Body disc brakes used Bendix mc as I mentioned. Any small booster was not Disc, but power drum on a B body in the year discussed.
Look up the Master Cylinder article, it will help explain.