Gravel drive or paved? Snow covered or bare? Smooth or rutted? Hilly or flat?
More rear ballast is always better for a heavy load, but if you have a smooth, level, paved driveway then you only have to lift the load a few inches off the ground. The centre of gravity will still be very low, and there's not much trying to tip you over. Worst comes to worst, you could even slap a couple of snowmobile dollies under the leading edge of the load or bolt a couple of utility wheels to the front of the pallet and let them carry some of the weight.
But if it is a typical unpaved farm lane, rutted and heaved from winter frost, I would definitely use the heaviest counterbalance on the 3ph available.
That's assuming you can even lift it at all, which depends as much on how long the pallet is as how much it weighs. Your forks weigh 220lbs and your pallet is 825, so your load is 1045lbs -- BUT that's not all at the pin. Heck, the back of the pallet forks are probably 6" to a foot out from the pin.
According to tractordata.com, you have quoted the full height lift capacity at the pin. That drops to 769 lbs at 500mm (about 20") forward of the pin. That said, the breakout force at 500mm is listed as 1634 lbs. -- I think that is a more useful number here. Depending on exactly how far out the centre of mass is from the pin, you may be able to lift your pallet off the ground somewhat (although you'll never lift that much to full height).
Depending on the height of the trailer deck, you may or may not be able to lift it sufficiently to unload it from the truck -- but that's going to be a real close thing. Like Jay said, if you can lift it at that height, get the driver to pull forward and lower it towards the ground before trying to move the tractor.
So if you decide to try it, make sure you have the heaviest end of the pallet towards the tractor, keep the load as low as possible, go slow and keep one hand on the joystick ready to drop the load to the ground at an instant if the tractor starts to tip.