> What would you name the parts? do_stuff1(), do_stuff2(), do_stuff3()?

depends on what the function does, most likely the best decomposition into functions isn't simply splitting the function in to n sequential parts

> I have seen very clean codebases with a handful very long functions, but they were no issue she nice they only did one thing.

one thing usually consists of multiple other things

imho length should correlate negatively with cyclomatic complexity - it's ok if you write 300 locs if all you do is fill a map with trivial entries