Other than the low-profile cab, there are two other details that will make this Atlas S-2 into a New Haven RR DEY-5: the distinctive whistle, and the cab control box.
As I may have mentioned elsewhere, the New Haven considered its diesel locomotives to be electric locos with their own on-board power plant. Stands to reason since the NH was one of the first major railroads to electrify its mainline starting in 1904. As a result of this attitude, many of its diesels were set up like their electric brethren, including everything from a similar control stand setup to the same Pullman Green and Dulux Gold paint scheme.
One of the other distinct features was the use of an air whistle instead of a more traditional air horn (a practice which was broken by the delivery of DL-109s with their Wabco E2 horns in December, 1941)
On the DEY-5, these whistles were mounted on the corner of the long hood, ahead of the engineer's side of the cab. While the exact position varied on the DEY-3 units (Alco S-1s, as pointed out here), on the DEY-5s, they all appear to be mounted just past half-way between the front of the cab and the first vertical rivet line.
In addition to the distinctive looking (and sounding) whistle, the New Haven also equipped many of its DEY-3 and DEY-5 switchers with cab signal equipment for road service (as detailed here). According to the Shoreliner article, eight DEY-5s received such equipment - and it just so happens that I was able to blow up a prototype photo of the 0604 to show what exactly it had.
As you can see, it's mounted on the engineer's side running board just ahead of the cab. It was at about this point in my research that I realized that, other than the cab, all of the NH-specific details were located on the engineer's side . . . and on my layout, the prototype orientation of the engine is typically showing the fireman's side. <facepalm>
And it works GREAT! The light comes through the lens and NOWHERE else - just like it's supposed to. In fact, it works a little too great. The bulb is so bright, it will literally burn your retina. Fortunately, I'll be able to dial down the brightness with some decoder programming. But I'll save programming for another post sometime...
For now, and with the lighting figured out and done, all I needed to do was to put everything back together and admire the finished product: