Using the Budd wrench is fun... until you do battle with rusted threads. There are impact sockets that are available for them:
http://www.amazon.com/gp/product/B000HI ... 00_s00_i00
Best price I could find. This is for a larger impact gun (my 3/4 inch impact wrench is rated at 1000ft/lb) but sockets for small impact guns are available.
First thing you should do if the inner nut doesn't come off with the Budd Wrench and a small, 3-4 ft cheater bar is:
MAKE SURE YOU ARE TURNING THEM THE RIGHT WAY!
Hit the end with a hammer to try and unjam the rust.
Now, try your impact wrench and see if it moves.
If not, heat the inner nut. I would not use MAPP or acetylene, only propane as the the other two's flames are significantly hotter and can alter the nut's strength.
There is a very real chance that if you use the Budd socket on an impact wrench that you can snap the head of the inner nut off. If you do, simply get a deep well socket *slightly* smaller than the outer nut and pound it over the threads of the inner nut at least half way. Use the impact wrench again on its lowest setting... of use the Budd wrench with a longer cheater bar.
If that fails its time to start cutting.