Waturi,
Since your car did not have power brakes from the factory, you will need to modify the firewall. Attached is a pdf file that shows the modifications required. My Cougar came with factory power drum brakes so when I converted to front disc brakes ( a very worthwhile upgrade in my opinion especially for a street driven car ), my firewall had already been modified by the factory. Also since you are switching from manual brakes to power, you will also have to modify the brake pedal hanger and install the power brake pedal. Also make sure you change your brake light switch to a brake light switch specifically made for the power brakes ( uses a lighter spring ).
Here is another thread that shows a Ford engineering drawing of the same modifications
Coach Jack
Booster installation template.pdf (140 KB)