To go with power brakes you may also need a new proportion valve to re-adjust the flow to the brakes. Depending on your donor parts, they may require new lines to/from the valve to cylinder.
A front disc brake conversion, requires a lot more than just calipers pads and cylinder. I don't have much time on my lunchbreak to find you a few articles to point you in the right direction. but here is one
In short you need to replace everything from the nuckles out to make it work.
There is alot of info on the forum about this specific topic. If you are having a hard time finding it through the forum search, try using google and included jeepforum (one word) in the search