This suggestion is about the North Berwick Line also with the branch off to Dunbar. Starting at Edinburgh Waverly, Calling at: Musselburgh and Dunbar, Or Calling at: Musselburgh, Wallyford, Prestonpans, Longniddry, Drem and North Berwick. Musselburgh has a short platform and can only fit 5 coaches. The trains are: The class 322 The class 380/1 The class 380/0
I'm going to add some of my local (to Scotland) knowledge here with this: The Class 322 & 380 did not operate this line at the same time. So it's one or the other. The Musselburgh platforms can fit all ScotRail trains that ran there anyway.
Excellent idea and furthermore if you own this route and Cathcart Circle the Class 380 will appear there as a layered train. German routes have this feature