Drop in a custom user model and
a) Better be a brand new project at all
b) You need to muck with the user manager also
c) How do you fix up the admin module? I have yet to see a
fully fixed up admin module for the custom user.
I am not a Django pro so happy to be proved wrong. But take a default app, and record all steps to make the user model work (including password reset, login, logout, admin page). If that doesn't feel crufty to you I am not sure what cruft is.