Please help the newbie here. I am converting my GF's old trek bike to fixed gear/SS. It has 130mm spacing in the rear and I installed a flip-flop wheel that is 120mm. I am now working on the chainline and I feel like I need new bottom bracket that is shorter to push the crank/chainline towards the center of the frame. The bike originally had 3 chainrings and no idea and what size is the current bottom bracket. I can see that the chainring is pushed far away from the frame.
Cranks have been replaced with a crank for SS/FG. 1 chainring only.
Could somebody please tell me what bottom bracket I should install to have a correct chainline with the flip flop wheel? Is it 68x103, 68x107? Any help is appreciated.