I didn't see a pic of the offending fitting but if you can get an "anvil" on one SIDE of the fitting and apply blows to the exact opposite side, against the anvil, the external threads will expand and the fitting will get loose.
The anvil can be a foot or so of 1" shaft, and may need someone to hold it tight to the side of the male part.
The hammer can consist of another chunk of shaft or a large punch, and struck smartly with a BFH. Don't be afraid to hit it several dozen times, always against the anvil. Rotate around the fitting as space allows, but always position the anvil opposite of the hammer blows.