Railworks America

Looks to me like it's pretty nice. The chute on the RWA is narrower but the one on the Allegheny coal tower seems to be about like yours so I say fine.

The H.A.E.R. archives at the Library of Congress are a good and free resource.
Historic American Engineering Records holds a lot of photographs and drawings that will help you re-create the steam era of the USA's industrial past.

Try a search like this: http://www.loc.gov/pictures/search/?q=coaling%20station&co=hh
Will give you a.o. these results: http://www.loc.gov/pictures/collection/hh/item/wv0321/

Original measured construction drawings of RR standard coaling stations might be available from their historical societies.

If the general proportions are right, being a foot off probably doesn't show in a freelanced model.

Is building an animated/interactive object like a water tower in Railworks like building a steam locomotive, or is it less of a nightmare? Are there any guides around the place for building turntables, coal loaders etc?