I make no apologies, Marklin American freight car prototypes are absolutely terrible. They run great but just about everything is out of scale. The wheel sets are huge! To add insult to injury, the trucks are mounted way to far in to accommodate the huge couplers Marklin uses. Why they spent a ton of money in tooling and went in this direction for American freight cars and F7 locomotives, I don't know. One exception is the tank car. It has decent detail on its dome superstructure. It also has a nice and accurate handrail. The upper works in general look to be in proper scale and proportion. Its the trucks that kill the car and make it look almost like a toy. So I bought the shim you can buy that allows you to install MTL trucks. It does exactly what its supposed to do and allows you to install MTL trucks and allows everything to clear. But it made the tank car look like it was on a lift kit. No added structural chassis detail to justify the high ride height. And at $18 a pop, it make for an expensive conversion for a fleet of tank cars that I would like to make. Tank car, trucks and shim kit adds up to $60+ when your done for something that looks just OK. So I decided to develop my own chassis. Needs a few more tweaks but this is what I have so far. I modeled it roughly after this (image off the web, credit goes to name on the image). I made it so I could easily add .31mm main air lines and the hand brake connection (slightly thicker silver colored wire). I did this so it would be more durable and the detail would be more crisp than if it was printed. I don't plan on running or displaying my tank cars upside down. So to all you rivet counters, the brake system is just the basics to add visual detail from the side and top views. I'm pretty happy with it so far. Made a few tweaks in the CAD file for another print that I should get in few weeks from shapeways. But this is pretty much what it will look like. Also need to fill in the old bolster holes and sand off the print on the top of the Marklin chassis on the next go around. If anyone knows where I can get better brake wheel, please let me know. The Marklin one is huge.