If the current BB still spins, then i'd just fill it with grease and keep it in there. Winter riding is tough on BBs- no sense replacing until you wear out the current one. If it currently has a mtb crank, then i'd keep that as well instead of using the 105- you can fit smaller chainrings on the mtb cranks.

If you can't get the chainline to work with the inside or outside position on the crank, you can get spacers to move it in or out the additional few mm you need. try sheldonbrown.com.