Master Cylinder Question

[348tripower]

Can anybody tell me the difference between  a power brake master cylinder and a manual brake one? I have a conversion here, a disc front and drum rear, with really hard pedal. Won't even move 1/2 inch.  I am wondering if this was a power set up originally and someone removed the vacuum booster?
Thanks,
Don

[phat rat]

Power has a shallow hole on the back of the plunger, the manual has a deep hole so that the rod doesn't fall out.