Easy peasy swap.
Putting together pieces or getting a kit?
Original V8 car or six cyl?
I put you over in the classic forums to get you some expert advice.
Welcome to stangnet
1. First, don't go for a "power disc brake" kit. People are never happy when they do unless they are using an OEM power booster and in the case of a '67 the correct power disc brake pedal. There are many kits out there to retrofit power brakes and for whatever reason they just do not work the way they should(I suspect they tend to ship with a master cylinder that is too small).
That being said, I am not aware of any problems with the manual disc brake kits. Before I decided I needed disc brakes though...ask yourself why you need them. Drums stop the car just fine, especially if you buy a decent shoe(which is not what many autozones and the like sell). If the car is a cruiser that sees occasional use, I simply wouldn't bother...you will get more mileage out of more defensive driving and a better shoe. If the car is a daily driver...then its justified, and if it sees any type of performance driving then its definitely a good upgrade....but no reason to waste time and money on something you drive once a month to the local cruise-in.
2. Ok, so you want disc brakes because you want to stop better. Research your kits that have ACTUAL DATA backing up the claim that there is a true improvement. An example, SOT's setup as tested by Hot Rod:
We install and test before and after effects of Street or Track’s brake upgrade for early Mustangs
www.hotrod.com
Anyone can say their setup stops better than stock...look for independent 3rd party verification with actual hard numbers.
3. Its not as simple as swapping brakes. Rotor size and caliper choice are going to affect the size of wheel you can run. In the link above, SOT's setup is a significant improvement even over stock disc brakes.....but, that setup requires 17" wheels to clear. You can of course step down in rotor size and maintain most of that performance...but that's a compromise.
Find some hard data, talk to people with the setup you want and see how they like it first, those are the key takeaways. There are plenty of kits out there claiming all kinds of wild things...verify their claims or risk wasting a bunch of money.