Some folks have been able to work the upper rope seal out then use a tool called a sneaky Pete to squeeze the new one back in. If that won';t work for you, you're going to have to move the entire transmission back atleast 3/4" inorder for the tranny's pilot shaft to pull out of the pilot bearing as well as some other procedures.
This Link shows the procedure to replace the bearings in-vehicle which is the same basic principle for dropping the crank to replace the seal.
