It depends on what you want as far as your brakes go. There are a couple of different options you can go with here. First, as Bill mentioned, is the vacuum assisted (VA) setup. This is going to have a couple of different things you are going to need. The booster, the bracketry for it, etc. I am not sure of everything because I have never done a vacuum boosted brakes system.
The other option is the hydroboost (HB) system. It requires you to have power steering. End of story, if you don't have PS you cannont do HB brakes.
Now, there are pros & cons to using both of them and folks who use one and not the other (or vice versa) will argue one way. I am a HB man myself for a number of reasons. The problem with both systems is that if the engine dies, so too does your power brakes. The advantage to having the HB over the VA here is that HB will revert back to manual brakes and will not leave you without a way to stop. Because the VA system relies so heavily on the vacuum, it will not stop as easily as the HB, even if the engine dies. That was my main reason for going to HB. Another thing is that I have disc brakes all around and VA doesn't push the pressure as easily that HB does (and the pressure that those calipers require).
But, if you look at this in a manner of what needs to be done first, I would suggest you decide on what you want to eventually do with this rig and work from there. If I were in your shoes (and I was at one time) I would start out with putting power steering on my rig first. Manual drum brakes can be adjusted so that you have more than enough stopping power with "minimal" pressure, for a non-power/disc setup. After you have the PS, then I would do front disc brakes, HB-brakes & finally add rear discs. That is the easiest and actually the most sensible way to go about it. Your current master cylinder will handle the disc/drum set up, but it will not handle a disc/disc set up. There just isn't enough pressure being created to push the calipers.
As for power steering, there are also a number of choices here too. There is the Scout box, Toyota box, the F-150 box, the 4x4x2, or the simple and easiest swap, the Bronco swap. You can get the needed parts from a 73-75 Bronco and everything will bolt directly in without any modification to mounting bracketry like all the others need. The only difference is that you will have to do some minor cutting on your inner fender & core support because of the steering shaft rag joint & the PS box is longer than the manual box. That is the direction that I would go.
Hope that helps you out.
