The 67 kit is alot different than the 65/66 kits.  The difference is the 67 kits are built using factory original parts so everything will fit right as it did from the factory.  The problem is there was always a real tight fit between master cylinder and shock tower on 67/68 Mustangs with factory power brakes.

If you will use the 67-70 power disc brake master cylinder, you should be able to get it in there.  It will be TIGHT and might require you to loosen the booster studs so the booster can be angled towards the engine slightly to get the studs into the mc.

A possible cause for interference is if the lower booster studs are overtightened, collapsing the booster stamped steel plate and the firewall into the plate cavity.  That causes the booster to angle downward a little, pointing it towards the wider part of the shock tower, lessening the available room.  If that has happened, it will need to be corrected.  Sometimes tightening the upper studs will even it out, but repairing any damage from overtightening is the cure.  The booster studs are attached with self locking nuts and they only need to be tight enough to keep the booster from moving around.  They are in tension when the brakes are applied.  Do not overtighten them.

Bough the 67 MC It was idenical to the Granada MC in size. Cut about 3/8" off each booster stud and got it installed, plumbed and bled