I've seen people do it before, but I've never seen anyone adapt the power steering pump as well. Usually people will do the hydrboost unit and the pedals, along with the hydraulic lines to make it all work, but the factory pump isn't the best choice for application. You end up with a very dead and stiff feeling brake pedal that also receives a LOT of power steering whine through the firewall, and the pedal movement is very choppy. I went through several stages of Hydroboost conversion myself, so I know how different things affect the car.
1. Hydrboost unit only: The unit didn't even line up withe holes on the pedal box or the pin on the brake pedal. The shop that was doing conversion butchered the install, hacked up the hydroboost unit to fit, put some spacers under the brake pedal cover, because it was not on the same level as the other pedals. New lines had to be run from the power steering pump into the hydroboost unit in order to make it all work. End result was a pedal that was ungodly hard, had a very short travel, and 0 feel. The car stopped really well, but it felt like complete garbage in terms of actual brake pedal feel. On top of all of that the notoriously noisy power steering pump would now feed all that noise right into the cabin because the hydroboost unit is powered by it.
2. Hydroboost unit and pedal box: I've chatted with someone at MM, and they suggested to take a look at the pedal box out of a hydroboost equipped mustang. Apparently the motion ration is different between the vacuum assist brake and hydroboost brake pedals, which would explain why the pedal box and hydroboost didn't line up on the first install. I had a shop swap in the pedal box, and had to buy another hydroboost unit, because the previous shop hacked up it beyond what could be used. The pedal travel increased a bit, but the pedal still felt completely dead, and there was still feedback noise from the power steering pump, not to mention the pedal motion would be choppy.
3. Hydroboost unit with pedal box and power steering pump: Whenever I would drive the car, I would think to myself, there is no way this kind of brake feel would be acceptable by an OEM application, even for a mid 90s american built car. A friend of mine had a stock 96 GT, so I asked him to take it for a spin, and sure enough his brake pedal felt nothing like mine did. It was much smoother, and it had slightly better feel, although still not as good as vacuum assisted brakes. I had to finish the hydrboost conversion, power steering pump was the final piece of the puzzle. The issue became then how to mount the power steering pump, because not only was it mounted in a different location on the modular motor, it was also mounted in a completely different style. I had a shop spend 4 billable hours and fabricate a custom mount for the power steering pump to put it in the stock location. I've compared the size of the power steering pulleys, and they were the same, so at least I knew that I didn't have to deal with anything being over-driven or under-driven. After the correct power steering pump was installed, the car finally felt more or less OEM-like. The pedal pressure was normal, no power steering noise feedback into the cabin, pedal movement was normal too.
C.N.: Hydroboost conversion is all or nothing type of deal. Unless your vacuum brakes don't work at all, don't do it. And if you do decide to do, don't do it anyway. Just sell the car and buy something better.