I'm looking for a Shimano BB-UN72 73mm x 110mm bottom bracket. Nobody seems to sell one for my Trek 4500. I replaced it 4 years ago or so and it's toast again. I also replaced the crankset with a Deore. If I can't find the BB can I replace both with a Shimano LX FC-M580 crankset. Will this work with my existing FD and chain?