The difference between the pedals is the mechanical advantage that the pedal creates when you step on it. If I remember this correctly, a manual pedal will have a higher mechanical advantage.
If the shop manual is correct (using a 72 Ford Shop Manual) then the physical pedal assembly remains the same between original power disk and non-power drum. Pedal free height and travel are different.
My car had manual brakes and I swapped to power disks. The power kit contained a longer pedal. Where the pedal mounts to a bracket on the firewall, there is a drilled out pivot point. There is an indented point on the top of bracket that you drill out in order to mount the pedal for power brakes. Look at page 3 of the following link.