Sorry to revive an old thread (still less than a year old though), but I'm also trying to convert an azuki to fixed gear and want to replace the bottom bracket. Posted in the mechanics forum with no luck. Here's a link to the exact model of bike (that I found on cl):

http://cgi.ebay.com/ws/eBayISAPI.dll...ayphotohosting

I measured the bottom bracket shell with a caliper, and it's 71mm wide. I even have a spare tange 68x103mm bb to test-fit. It screws in fairly easily, but it's pretty tight so that the spindle doesn't rotate freely. Has anybody changed the bottom bracket on a similar Azuki? Do you know if a Shimano Square Taper BB Italian 70 x 107mm (UN54) would fit? Thanks in advance for any help!