Long ago...far away...
...I modeled trains in HO scale...
About 1990, Athearn released a model of this carbody. It's called a "Pre-1980."
CSX Photo Archives has practically every model of locomotive from all the Fallen Flags on this page, you'll see that the Family Lines System ordered 163 locomotives from #8000 to #8162. The model starts a #8087 & runs out with #8162 where older Louisville & Nashville SD40-2's start.
The order was changed along the line somewhere to Seaboard System, however I new somewhere up at about #8085 or so the carbody changed.
Modelers have often mistaken the bulge in the db housing for 'extended range db' & N&W did receive a fleet of these locomotives with Q-fans, no bulge...they may not have had an exhaust silencer...or the housing was re-engineered later...it also cost more money to fabricate this type housing.
Farr louvered radiator & intake grills are another characteristic of this series.
As I mentioned, Union Pacific & also the Santa Fe received orders that had the db bulge, exhaust silencer & Farr grill, however I believe they were also "snoots," with Locotrol installed in the nose for mid-train radio controlled engines.
The Canadian roads were the last holdouts for SD40-2's, with "Draper-Taper" carbodies at the end of SD40-2 production, then the "Super-Series" GP & SD50's began production.
I think several other Mods are holding off EMD units for the rest of this year, so If your interested, you might beat them to the
punch...!
Either way, now you know...!
or ill have to go by csx_or_bust lol
My god! That's incredible, let us know when your done! 
Nice! Very Nice!