I too have a L59 mower on my "B". I just changed blades and am having quite a time getting the belt back on correctly. It seems like the belt is too short. The two adjustment pulleys near the PTO pulley are all the way at the top and I have to really pull to get the belt on. There's no need to adjust the pulleys because it's tight as soon as I get the belt on. Is thishow yours works?