Most likely your alignment guy has run out of adjustment with your tie rod ends when you have your steering wheel perfectly centered in the car. I fought this nightmare for years with my '55 C300. When I had my steering gear rebuilt I thought that might help. As you can guess, no difference.
Your F may have a different design from my C300. However, the concept may be the same. Pull the steering column and move the connections to the steering gear a couple of splines from "original / stock " position that will enable your alignment guy to have a full range of adjustments with those tie rod ends. Unlike me, make sure you move the splines in the correct direction the first time or you will get to do this job several times. None of this would be necessary if our steering wheels were not keyed to fit the steering column only one way.
Good luck!
Bill Allen