In the right hand photo. On the outside track, there's a join with some broken sleepers, at that joint I'd put a right hand turn out in there.
Set right, the train continues on your original track, set straight, it picks up the new.
Having seen the photo's of the original OP's loft, I'd say forget it. I have same/similar cross timbers in my loft and after having to climb over - dive under them about 20 times, I promise you get fed up with it!
Will be looking to build a shed at the bottom of the garden soon and move down there.
Was watching a Class 24 with sound, the listing ended unsold at £149.00 + £8.00 p&p. The seller relisted the loco, £165.00 plus £8.00. If it didn't sell first time round at that price. . . !