I just did a Google search for "plans for Chama coaling tower". I got ALL KINDS of hits-most for 1/20.3, but you can easily do the math for what you need.
Here is a great link for a website which has alot of info on coaling towers in general. It's pretty good for info, but it dosen't cover chama, although chama isn't far off from standard gauge practive. Here's the Link. Cheers
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