Smoky,
It sounds to me more likely that your tractor needs a tie-rod end than a "steering head", especially if your front wheels are no longer tracking in parallel.
If you have manual steering, the steering wheel moves something (a pitman arm or a rack) back and forth. This moving part is connected to each of your wheels by tie-rods. At the ends of these tie-rods is a small ball-and-socket joint called a tie-rod end. If one of those joints fails (e.g., the ball is worn out and comes out of the socket), then your front wheels will no longer track in parallel.
If your steering is purely hydraulic, then a hydraulic cylinder may be attached to one front wheel, with a long tie rod connecting that wheel to the other. There will still be a tie-rod end involved which may have failed.