Well, at the top of the Shimano Tech doc brought up by the search I suggested, it states that the BB-5500 comes in a 68mm size. You could measure to be certain.
http://techdocs.shimano.com/media/te...9830612168.pdf
It really seams that a frame swap may be beyond your mechanical knowledge or experience level. You may want to consider having a shop do this work for you.