Substitute brass for iron where ever you see it, as the model is built in brass, but the original is in iron, as also the look of the model will be when finished. To build in iron is very simple, unlike timber, as the materials are already of the correct basic dimensions, thickness and shape, and there are only 3 of them, angle iron, plate, and bulb iron.  The complications come in the working of them - with timber it is an adze, saw and boring tool for basics, and each piece is worked on i