Mot likley an Impact wrench wont get it off. It wouldnt get mine off and I used a bad ass impact wrench. I was lucky enough to have the engine out of the car when I did it with the tranny off. The new engine came off of an automatic and it still had the disk where the flywheel should be so I wedged a screwdriver thru one of the holes in the disk so it would'nt turn and I had 4 people hold the engine down and I used a breaker bar with a six foot extension. It did break loose but it took everything I had to break it. You will need a lift. Your gonna have to raise it up and get under it with a breaker bar while sombody holds the break with it in gear.

i did it using the starter power...just be very careful!