Thanks for the help. Is the UN73 a direct replacement for the UN72? I have not been able to locate a UN72 on the web and all references seem to direct me to the UN73. I would think that there would be a spindle replacement for the Twenty's BB. I seem to remember a bike shop taking a shimano 105 sealed cartridge BB and threaded it into a 60's Raleigh Gran Prix I have. It worked but I don't rember if the threading was the same as the Twenty.