I started with an Atlas GP40-2 shell and grafted in parts from a GP50, Intermountain SD40-2 and a Kato SD40.
The radiator grills came from a GP50, the dynamic brake area is GP40-2 but elongated with mouldings from an Intermountain SD40-2. The exhaust is incorrect (how did I miss that!!) it should be a flat bit of styrene!!
The dustbin is Kato SD40, the T vent is from a Kato F40PH.
The air filters are from a GP50.
The rest is styrene.
Basically you remove the top of the GP40-2 shell and rearrange everything.
This is not an exact replica but it's the best I can do right now. I had this posted before when I was constructing it hoping Robbmann would critique it ;D