I don't think they come off the hubs on the 150's. Check with the parts dept. at a Ford dealership to see if they are offered seperately. My shop works on them all the time, and I just can't remember right now.
I know the 250 does come off. If you heat it you will heat everything and have to repack and replace seals.
Have you pulled the hub and rotor assy?? If you take it off you can press them off