Joe,
I have been working on a Flint and Walling mill lately and have messed with a couple of others. So I'm no expert and I haven't gotten the hub off of my F&W... yet.
The smoke wrench (AKA oxy/acetelene torch with a rosebud) is your friend here. Try that and if you have an impact hammer use that on the end of the shaft. The vibration plus heat helps to loosen things. You can also drill the key out, lock the mill up and then try to twist the hub on the shaft. Don't be suprised if it takes a number of heat/cool cycles to get it to move. Use lotsa penetrating oil in between sessions.
If you use a puller you need to be real careful, cast iron is brittle. I have been trying that on my F&W and haven't broke the hub but haven't gotten it off. The key on this mill is an odd, wedge shaped one that is an extra pain in the a$$. Just keep at it, it'll give it up.
Jonathan