removing pinion seal

I am getting ready to change my pinion seal in my 8 3/4 2.76. I pulled the 3.55 (389) and am replacing it with a 2.76 (741) (is the original)- it's already out of the rear so What is the best way to secure the chunk to losten the nut ( the torque is aroung 400 + pounds) no/yes. My 3.55 is great but not for just bumping around town. Good idea about marking the nut location. Thanks
Dave