The issue is cutting and welding it so its in line and should be done in a lathe to keep it all perfect. you dont need it to be balanced but it will be much nicer to the rest of the drive train if they are.
Way back when i did my yellow yj i went to fleet to modify the front shaft and they did a fine job. Of course, it was wrong still but it was my fault, so we cut it apart and hacked it up at Aarons house one night and i used it for a few wheelin trips. Then i ordered a whole new one from High angle with another flange like i did for the rear shaft.
