Similar situation in my field - twice.
Used a flat piece of granite in the muck to support a jack, disconnected the brush hog and pulled it off the rear by hand, woo. The granite will sink then stop when it hits solids, giving you a jacking base. Then slipped a sheet of plywood under the front wheels as far back as possible under the tractor. Jacked up the rear, one side at a time, and filled the tire depression with evergreen bows in front of the rear tires in such a way as they would get sucked undfer the tires. Believe me, mine has been down low in the muck, over the rear frame. SO basically, I lifted the tractor on plywood and drove over it. Once iot starts moving, keep the pedal steady from spinning and keep going !
So first thing, low range, start slow, the FWD will pull the front tires forward on the plywood after a little rocking f-r, the rears will get the brush drawn under them and enough to get a grip on the plywood that under the tractor.
1st time took me 4 hours, 2nd time lessons learned, less than 1 hour. My field changes so one year dry, next year soup under the field grass - you can't see it till your're in it, and then you're
screwed.
hth