Hi Matthew,
The T. E. Haynes "Hot Air (Stirling) Engine" or "Steam Engine & boiler" might be two engines worth considering. I've made both, and quite achievable with a lathe, a milling slide, a pillar drill and some silver soldering equipment.
While the HAE requires a cast base, I just fabricated it from aluminium plate and a couple of blocks dowelled and screwed together.
The only obstacle might be getting hold of the books. For whatever reason, they tend to be a little pricey.