I have struggled with those stout original style national seal metal housings as well. They are unusually strong compared to new made seal housings and hold into the hub very tightly. Removing them even with a ladyfoot is difficult as it is hard to keep the entire drum/hub assembly from moving while trying to lever out the seal.
What I found to be the holy grail with this is amazingly simple. Instead of trying to pull the seal out from the inboard side, I drive it out from the outboard side. There is about 1/4 space between the inner bearing and the seal. I made a simple "seal driver" using a short length (approximately 12-16 inches long) of heavy walled 1 1/2 inch pipe and welded a round 2 1/4 inch diameter x 3/16 inch thick plate on one end of the pipe (a large thick washer would work). For removal: 1) support the drum/hub off the floor with some 2x4 pieces so that the seal is not touching the boards or floor, 2) place the lip (washer part) of your "seal driver" against one side of the seal and strike with a 3 pound hammer, 3) repeat step #2 about 180 degrees from the last strike and hit it again, 4) smile at how easy it was to remove. Only takes two well placed strikes to remove.
