I think you are referring to one of my scenarios With a tweak in my ini file (i am on PC), i can Spawn single coaches or multiple ones, even said Mk3s without the Class 43. Surprisingly, the Mk3s have a working buckeye coupler despite never being (un)coupled in the game normally. Thats why a Class 66 can couple to them and so its possible to have a bunch of Mk3s Pulled by a 66 as loco hauled train. And because those special formations like the single coaches doesnt need the mod to appear in a scenario, just to place them into one, it works on consoles via Creators Club too.
