The only way the u-joints could get "out of phase" would be if the drive shaft was cut for some reason (shortened or lengthened) in which case keeping the joints exactly as they were installed is very important. Since both u-joints are welded to the drive-shaft they can't move so you don't have to worry about them. Every yoke I've worked with could be installed at any position of the tail shaft. So just slide it off, be ready to catch any fluid that leaks out, replace the seal and slip the shaft back in. Good luck.