Good call on sending the booster out for a pro rebuild.
Adding PS will be a bit of work but can be done using original used parts or with a "modern" rack and pinion system. Google should find some suppliers for you as well as the Thunderbird parts suppliers for used. Worthe Enterprises, and Flaiming River come to mind & I'm certain others have parts available. Another issue is having an available unused groove for the belt on your crank pulley. Hard to tell in your pictures but do you have one behind your existing belt? You have very little room between your crank pulley and the fan motor from your pictures to change the crank pulley. Since you have a later engine, you should be able to locate brackets, pulleys and a pump to fit from what ever vehicles the donor engine came from, so you may have to put the fan in front of the radiator.
Solving these problems is just part of the fun of modifying an old car!