A really good place to start on the early (really early) stuff is the two books produced by the Early Railways conferences, 'Early Railways' is ed. Guy, "Early Railways 2" is ed. Lewin, both are published by the Newcomen Society. Have a word with your local library - they might be able to track them down. As well as articles, drawings and a lot besides, Early Railways
2 has a chapter on the start of railway preservation in the Patent Office Museum, South Kensington - this structure, known as the "Bampton Boilers" was one of the first big iron public buildings. It's fascinating stuff (I reckon). Recommended, and don't blame me if you end up modelling a scene in which these new, hyper-modern Stirling singles are displayed alongside the newly-preserved relics ;)