You can save yourself some time now if you still have the cover off. Just cut the lip off that the "old" seal presses up against and use a newer timing cover seal. The new covers allow for installation of the seal after the harmonic balancer is removed. Just FYI.
I changed my timing chain and gears today, boy was there some slack! I would change them while you are that far. Carefully pry the thin metal away from the timing cover all the way around the seal and it should pop out.
They aren't quite interchangeable. The newer covers can't take a dipstick. If you were to try drilling a hole for the dipstick, you'd hit a water passage. Ford does/did have a service part for the older trucks that takes the front installed seal.