It sounds like a lot of your questions have been answered, but just to add my two cents... for the complete picture, definitely e-mail Christopher Howard:
christopher@railflyermodelprototypes.com. One of the main things Railflyer has going for it is that you can contact them and get a quick detailed reply, from the owner no less.
Also, check out the building resources site:
https://sites.google.com/a/railflyermodelprototypes.com/building-resources/ a number of us have posted photo's, build descriptions and instructions there, as well as prototype references.
Using a combination of mediums is really going to make these components stand out, Josh' description of the plastic hood core is spot on, essentially what you'll get are the good things about brass and plastic with fewer of the bad things. For example, the side sills pilots and steps are brass and are very strong and exactly to scale, other things though, like the knuckle busters on the hood are plastic so that you get the correct depth, something that is difficult to achieve with brass. I am working on a set of hood doors right now that will illustrate this concept nicely. I'll post some photo's once I've got them finished.
The trucks are currently under development and are expected to be really nice, scale width, equalized, with traction motor details, and possibly rotating bearing caps. They are still in an early stage though, so that's about all the info we've got.
To answer your original question about SD40-2's, the ultimate goal will be to offer a complete locomotive. Right now the concentration is on the EMD Dash 2 line of 4 and 6 axle diesels, but there are some components available for non-dash units (such as tread) and things like the frames and fuel tanks can be easily modified to fit almost any prototype size. Christopher formally announced Spartan cabs, and Stanchions last night, so hopefully they will be release shortly after the hoods. The Canadian wide cab is available now and the spartan cab will be similar in design. Cannon Cab's would also work fine if you don't want to wait for the Railflyer part.
Soon, it sounds like we'll be able to pre-order a full package that would include all the parts necessary to build a locomotive, which would then be shipped as they become available.
Before you go about ordering any parts, I'd recommend doing a very complete search on the various prototype photo sites for the locomotive you'd like to build. Try to find photo's of all sides of the unit if possible. Photo's of sister units which were part of the same order and were assembled at the same time can be helpful too as many of the basic details will be the same. Figure out on your own which Railflyer parts are correct for your prototype, then ask Christopher to come up with a list for your unit as well. Correlate the two lists and double check any differences. When I ordered my units Christopher caught some things I had missed, and I found a few he hadn't noticed. It sounds like a lot of work, but it's pretty interesting, as you suddenly begin to notice a lot of little details that aren't obvious unless you're specifically looking for them.
I hope this helps, if you have any further questions, don't hesitate to ask.
Chris
httP://milepost15.wordpress.com
