I converted from manual all-drum brakes to manual front disc brakes and rear drum from a 1971 donor. I am sure glad I did that, manual brakes on my CST/10 has a great brake feel and does not require much pedal effort. It took research from members 54blackhornet, Keith Seymore, and several others to figure out the master cylinder specs and part availability.
https://67-72chevytrucks.com/vboard/...39#post9169739
As far as i know, nobody has concluded on factory brakes how far from the pivot of the brake pedal lever is the attachment for the push rod and if it is really different for power vs. manual.