Prob gonna have to put vise grips around the outside. I believe you need to pull up from the front end like your going to lift the machine. Both mine and my dads was like that. I just used channel locks on mine it was easy, but using an Allen it wouldn't budge. Mines an XP I had to remove front clip to get to it good.
chisel and a hammer and give it a few whacks on the outer edge,or drive a torx socket in there and break it loose,good pair of channel locks..lots of ways to do it! I would take the diff out u can get to it ALOT easier!