Any idea why it is seized? Estate sale, sat idle for many years causing engine to seize? If this scenario is the case, you might remove the injectors and pour some marvel mysterial oil into the cylinders, let it soak a few days, they try turning motor over, working it back and forth in small increments. No idea what kind of drive your tractor has, if gear drive, you can put the trans in lowest gear and try to work the engine back and forth by gently rocking it forwards and backwards. Hydro would require using flywheel, drive shaft, or crank pulley/bolt to work it back and forth.
Good luck!