I'm a little confused by your story but I gather you want to put a 105 hollowtech crank on a bike with a threaded BB. You should confirm that the BB is 68mm wide but a normal Shimano external bearing BB is what you need - no adapters. $21.

Shimano BBR60 Ultegra Bottom Bracket > Components > Drivetrain, Brakes and Pedals > Bottom Brackets | Jenson USA