The Kato SD40 is a well-engineered model that both runs well and looks great. Features such as separately-applied MU hoses and number board inserts result in a very impressive piece of N scale machinery that also pulls well. Conrail has a fairly sizable fleet of SD40s, so if you're modeling the startup through the early 1990s, you could always use a CR SD40 or two. They're readily available and affordable. I picked up mine at M. B. Klein's in Cockeysville, MD on my way to CRHS's Spring Rail-B-Q in May 2009. This is part number 176-2003.
So, besides installing the separately-applied parts, there are a few easy things we can do to make this loco look even better. The next photo shows what we'll start with. That's a sheet of 1/16" styrene; we'll use that later. The decoder is Digitrax DN163K1B.
The first thing we'll do is to take apart the locomotive. I know, I know... Why? It looks so nice in one piece! Well, the good news is that Kato designed the shell in subassemblies. We'll use that to our advantage. We'll want to separate the chassis from the shell and the walkways. Additionally, we'll remove the cab (being careful not to break the handrails; they pop into little holes in the cab) and pop out the clear plastic from the windows and the headlight. This will make painting, weathering, and Dullcote application much easier.
I installed the decoder; this is incredibly easy following the instructions that came with the decoder. In fact, no screws or solder are required. However, I found that the decoder can come loose as it's essentially held in place via pressure; you may want to use the additional Kapton tape to secure it in place. I programmed and tested the chassis before I moved on to the shell.
The subassemblies look like this (here I've replaced the stock light board with the Digitrax decoder):
Now the fun stuff. Think about what makes a loco look Conrail... besides the blue paint and white can openers. The first task is to paint those safety rails white. I use acrylic craft paints for this, but regular model paint works too. The next thing I did could cause a fistfight at a CRHS meeting, but I went ahead and did it anyway. I painted the walkways black. Photographic evidence suggests in many cases the presence of a black skid-proof coating on some locos whereas others show blue below a coat of grime. Either way, I like the way the black walkways look. At this point I chose to correct a shortcoming in the Kato model... The prototype locomotive, CR 6324, had the can opener stripes on the left side extend over the blister and all the way to the cab door. Kato's stops at the blister. So, I used part of a Microscale CR diesel loco decal sheet to continue the stripes to the cab area. The stripes matched up surprisingly well. At this time I also chose to paint the headlight housing on the cab gray in accordance with the prototype as she appeared in the early 1980s. To our good fortune, in the early 1980s (I model 1980), 6324 did not have a snowplow, so the Kato pilot is mostly correct. Now's a good time to install the number boards and the MU hoses.
A true signature Conrail detail we will need is the cab signal box on the right porch. Sunrise Enterprises once made this part in N scale but no longer does. This is not a bog deal because the part is not that hard to reproduce. Go ahead and grab that scrap styrene. IÂ essentially reproduced the Sunrise casting (left, below, cast in pewter) using a similar sized chunk of styrene and some scrap brass sprue from some brass detail parts. I scored the box lid with an X-acto knife.
Painting this box to match the locomotive is difficult. I used a mix of PolyScale Conrail Blue and D&H Avon Blue but wasn't really happy with the result. Thankfully we'll be weathering the locomotive, so those subtle color differences won't be as noticeable. Once the cab signal box is mounted, it will be time to weather. You'll note in the photo I'd gotten a little ahead of the game with weathering.
 
I use acrylic craft paints following techniques perfected by Rich Yourstone and Tom Mann. One thing I do before I weather is to Dullcote the subassemblies; not only does this kill the shine of the plastic, but it provides a surface with a little tooth for the weathering. I masked the chassis above the fuel tank so as not to get Dullcote on the decoder or into the motor. This is also why we removed the plastic inserts in the cab; otherwise we'd have a dull glaze over the windows. This isn't Penn Central, after all!
I used washes of raw umber on the chassis (fuel tanks and trucks) as well as on the front and rear pilots. I used a wash of black and burnt umber on the shell, with emphasis on the fans and the roof. For the grills, I apply straight acrylic black and then buff it away with a paper towel to give the appearance of depth. This is where prototype photos are most helpful; merely slapping dirty paint around the model doesn't produce a convincing result. I used photos from the Fallen Flags website to guide my weathering for this loco. CRHS also has an enormously useful photo archive. I actually weathered the engine in subassemblies; this made it much easier. I also painted a few details like the running lights and fuel caps just for additional fun. Once the subassemblies are weathered, it's time to put the engine back together and put it to work!
This project took just a few hours spread over a couple of evenings. I found it very enjoyable and not particularly challenging, but certainly enhances the locomotive beyond its out-of-the-box appearance. It's also a bit more authentic to Conrail. I may also add a Sinclair radio antenna to this engine one day. But for now she's hard at work paired with an ex-PC paint-out SD35 hauling coal on or on a hotshot freight on my N scale Juniata Division.
 
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