A and B plan worked well. The crew and train always did the same thing. A train would load and back into track 2, awaiting arrival of B Train, then go north to AC. When B Train was loaded it went North to AC. At AC, A Train would arrive as normal at the station, the locomotive cut off and run around the train, and wait for the arrival of B Train. B Train would always take the siding at AC, and continue North until clear of the North AC switch, and then reverse down the Main to the station after the departure of A Train. The locomotive would then run around and then procede south when ready.
3 locomotives was the trick. The southbound train would pull all the way in at Sheepscot. The next locomotive in rotation would couple on and depart when ready. Depending on which train it was is what was done next (proced to track 2 or AC), so the locomotive crews had to pay attention.
Once uncoupled, the locomotive that just brought the southbound train in would move to the run around when the train was clear, and do it's servicing to get ready for the next train. The locomotives would have 2 successive trips, then a break of 15 or 20 minutes, awaiting the A Train.
This set up worked very very well.