I’ve only built two engines. Both simple wobblers. One from bar stock, the other from a casting kit. Neither very exciting.
I bought these two books from Tubal Cain some years ago and finally got to reading them. Very good. I really like how much goes into each one. So much better than a “machine these five parts and assemble and you’re done”. And you get to build a boiler for each.
“Building Simple Model Steam Engines” and “Building Simple Model Steam Engines Book 2”