First you should have installed the pinion and got the proper crush on it before anything else was installed,you can't measure the proper preload if your trying to turn the ring gear, the seal should not be installed untill you set the preload, then remove the yoke,install the seal and reinstall the yoke using locktight on the nut. They also make an E Z crush sleeve that you can do with your impact,
sometimes those are a little hard to find but check with your local auto parts store