I left a note in the welcome section for you also.
I am - as well as Dave D - looking forward to seeing pics of your 351ized 57.
We are pretty limited on space when it comes to adding a standard booster with the Master Cylinder on the end. At least with the Y-Block. Another thing that limits us of course is the way the hood opens and the latch bar. Pics of yours would be nice to see how it all fits in there.
Most here have gone to the Scaredbird adapters and I believe that is the way to go also. Parts lists come with those brackets which helps to source the parts like rotors etc locally. The Granada/Maverick/Versailles spindles are getting hard to find and do take a lot more work.
I have not talked with Old Irish Dave (OID) about what he has but that is a good suggestion. I will call him also as I am about ready to do the disc conversion myself. Dave D mentioned in another thread that he also has a good price on the proportioning valve that you will need also.
The kits that can be bought from the Tbird vendors utilize the stock booster so it will work but as Dave D said it would be better to have a more modern (and new) booster.
Dave D also has a tech article that outlines the Scarebird conversion from one he did. He also has some good info here:
Plenty more to come but that should get you started.