The GS-4 was not a Vision Line engine.....just a plain old Legacy engine. I was once on a BM&R #425 excursion, when they stoped to turn around a couple guys got on top of the engine and changed the whistle. When I asked why they said someone had brought it and wanted to hear it so they hooked it up. Goes to show you when people talk about engines having the correct whistle I tend to believe it is BS I can’t carry a tune so why should I say a whistle is correct. As long as it makes the hair on the back of your neck stand up that is all that counts.