No need to pull the bell housing. You can pry them out pretty easily without damaging the bell. You can't get to it from behind anyway due to the way the bell is machined. You will see what I mean when you get one out. Something that may help a little but not absolutely necessary is to put the seal in a freezer for a while ahead of time. Also be sure you don't leave any burrs on the edge from prying out the old one that may keep the new one from going in smoothly.