Thor,
First of all, I'm pretty sure I have a set of detailed pictures from 278 that you took. If so, thank you very much as this has helped me more than I can explain on building our models!!!
As for build info, I started a website several years ago that I just never finished. I tried to make it "cool" and "hip" but in the end it just was a little too odd for my liking, so I never published it...
We do have an article in the "Narrow Gauge and Shortline Gazette" Nov/Dec 2012 volume, that shows and explains much of our RGS 42 build. We have yet to write one on the 318.
We started with steel frames. At the time we didn't have the machinery / tooling to really accomplish a steel frame build. We then had aluminum frames laser cut. Afterwords, I found a problem with the plans we had, and on top of that, we didn't like how flimsy the aluminum was for a long chassis of a C-17/18. We later had Brass frames waterjet cut, and absolutely love them. These have a strength that resembles steel, and a machinability that doesn't require special cutters. On a smaller frame like what you are doing, you probably wont have any issues and I wouldn't worry about it.
As for drivers, We first tried home casting RTV plastics and they worked fine in the beginning. Once they got hot (like left in a car), the plastic would try to expand, but not be able because of the tires. Then they would shrink down and the tires would fall off. I'm not sure how 3d printed centers will work, but this technology was not really available when we first built our models. We switched from a plastic to a low melt tin/bismuth metal that we poured in a silicone mold. In general they work fine, but if you are off in pressing the tires, or the axles, or the crank pins, you have to make a new center. You get one shot with each. Both our engines have a "questionable" driver that will have to be recast to fix. We will try our hand at home brass casting on our next engine...
And finally, I cant really help you on groups or forums dedicated to scratch building. There is Large Scale Online (LSOL) that some people post pics and info on builds, but not many locos. Most all the knowledge we have came from either machinist forums, youtube searches, google searches, or friends in clubs (Like the NMRA), or magazines like the NGSL. We were building an almost unheard of scale, and couldn't rely on the majority of resources available to others. My brother and I are more than willing to help out in any way we can, feel free to pm us and I will send you our joint email. We don't check it every day, but love to share build info....
Casey
