I would skip trying to loosen the fitting without heating it.
I would not use a rosebud either, a #7 welding tip would be easier to control the heating of the bung. You want the bung to heat up but not the plug. Heating the bung alone with shrink the metal away from the plug after it cools.
Do not use brute force alone to break the joint loose as it could pull the threads out of the bung. When the metal cools enough to melt wax instead of producing a big cloud of smoke, melt some candle wax into the joint. This will help to lubricate the threads.
Do not strike the pipe wrench, it is better to strike the plug. You want to introduce the shock into the fitting not the wrench. Unless you own a 48" pipe wrench, you do not want to beat up someone else's.
If the fitting does not budge after heating and cooling heat it back up and than try turning it out. Work the joint back and forth to prevent the threads from galling.
Check the sealant used on the joint, if it is very hard like rock it is probably X-Pandohttp://www.xpando.com/xpando.php
To remove it you MUST
heat both parts of the joint red hot to break the grip on the threads.