The BB-UN 71 bottom bracket will not work with Hollowtech cranksets as it is square taper. Hollowtech cranksets require splined Octalink bottom brackets. However, Shimano offered Octalink bottom brackets for the 105 Hollowtech crankset that will fit this frame. The matching cartridge bottom bracket was part number BB-5500 but you can also use the Ultegra BB-6500. There was also a compatible Dura-Ace bottom bracket but it was not cartridge style and many members report difficultly obtaining proper adjustment.

Make sure you buy the correct version of BB-5500/6500. Your frame requires the English version (68mm width, 1.37 X 24 TPI threading) as opposed to Italian (70mm width, 36 x 24 TPI threading) . Also, depending on the number of chainrings, you'll have to choose between two lengths (109.5mm for double, 118.5mm for triple).