Class 378 Capitalstar (you have the gen already in TS Classic) to operate on the East London line for London Overground. I suggest West Croydon or Crystal Palace (slightly shorter) as the starting point, and end of the line Highbury and Islington. This is where London Overground naturally terminates before changing trains onwards. For a good part of this run we would share the lines with Southern 377's, Thameslink 700's and SE 375's all of which are either already in the game or will be soon (wink wink). So would layer very nicely indeed. A bit of the line runs underground too for a new challenge. Also after Whitechapel (incidentally where the Overground goes underneath the Underground!), there are good views of the City skyline. I think this would be a great addition using date you already have for the 378.
This is easily done with BKL Queens Park to Harrow & Wealdstone since that route is part of Watford DC Line
