It fits with a tandem master cylinder with over an inch to spare.  And works like power brakes are supposed to,  not just an add on booster.

Yup...what these guys said.  And, it's so clean it looks like it "came from the  factory that way".  And....it works like a charm.

BB

If you look at MS's photo you will see that he has an export brace.  They are higher and futher away from the master cylinder than the stockers.  Use one of those.  You should have one anyway for added rigidity in the front end.

I'd say an export brace, while not required is a no brainer super cheap upgrade that makes a lot of difference - the following is an intersting thread from Stangnet testing the effectiveness of different reinforcements on torsional rigidity of a '67 chassis.

http://www.stangnet.com/mustang-forums/threads/torsional-rigidity-test-67-coupe.723029/

As far as the booster goes I definitely recommend Mustang Steve's setup. I can also recommend his roller bearing pedal support assembly - it utilizes a plate across the front of the assembly that provides a solid mounting surface for the booster tying the booster/MC to the pedal assembly much more effectively than just relying on the thin firewall to hold everything together - it will ensure a consistent relationship between all the parts of the braking actuation system. Don't know if you're running a clutch but if so the added bonus of rock solid pedal location & perfect movement for the clutch pedal is well worth the price of admission.

ditto on what these guys said.i put a 7 inch booster in without changing the pedal assembly.i could never get any sort of good brakes.i got the pedal kit and booster from steve and  got better brakes than my newer truck.this mod if worth  doing!