If the bb you removed is a BB-UN52 than just replace it with a similar one or a BB-UN55 in the same spindle length. BTW, the UN52 is not original to those bikes. They came with Tange cup-and-cone bbs so somewhere along the line the OEM was replaced.

Remember that frame is aluminum so use LOTS of grease or, better, anti-seize on the bb cup threads.

Edit: I just saw Deacon Mark's recommendation and it has merit. A Tiagra crank, either double or triple, plus a Tiagra or 105 level external bearing bottom bracket can be had for $100 or so if you look around.