Any way to get some 2" thick planks under the tracks and skid them?

Are the brakes rusted on to the drums, heard of that plenty of times. Why not crane them on to a trailer, I've done that a few times, only costs a couple of hundred bucks, or get a tilt tray recovery truck in, the ones I've used to move Cats have had smooth trays.

From my own experience, back the brakes off if they appear to be stuck and whack the bands with a long drift or bar to see if they are loose; tie the steering levers back;make sure clutch is in the disengaged position.
When pulling with a chain, best results have been from chaining halfway behind the front idler and the carrier roller or sprocket if the blade is in the way. Chain to a pad in a "Y" pattern and heave ho with the other tractor. Many times that provides enough leverage to snap things free. Repeat on the other side .
My first D4 recovery was almost futile, as the IH 884 4x4 wheel tractor just dug deep and did not even budge the crawler; I felt as if that old 7U was determined to stay where it was and die in peace. I did what I just recommended and it broke free just like that. The previous owner drilled me for 1/2 an hour demanding to know if I had hired a crane or what, as it turned out he had 3 JD 6420 4x4 wheel tractors chained to it and could not get any results. His only reason for selling to me cheap was because he did not expect me to get it out.
I also bought a 15K Hyster forklift from Brewzer once, just so I could recover a machine that would not roll. Easy on, easy off. JM

franna mobile crane or tilt-tray tilt tray is probably the easiest and cheapest. remember smooth steel on smooth steel will skate. so if they could get some steel plate or box section under the tracks to for a skid(weld it to the grousers) you could skull drag it up on to the truck would need pulley blocks though to get enough pull.

I second the hooking to a pad. It effectively doubles the force on the track it is hooked onto.

My method with that would be to cut a bunch of wood rollers, maybe 20 or so, about two feet long and 4 to 6 inches in diameter from a small tree, start putting one in front of each track as it approaches the trailer, as you are pulling the cat and go under the tracks they will help it move and lift over the cleats, keep adding rollers every foot or two, will also help on the unloading.

I use 2 inch dia pipe rollers to move boats around on a wood plank on a lower wood plank

yes other have suggested the pipe roller shuffle. that requires getting steel plate under the tracks first and enough strong hands and bits of pipe to keep enough pipe under the machine. it does work but its laborious.