For what it's worth, one bit of example code using our ACME Python library can be found at certbot/http01_example.py at 459a254aea3a9a5a6ac9f069ba446d93ce307a5c
That's what I needed. With that example, I was able to re-write my client script to work with ACMEv2. The only significant issue that I hit was the "missing account URI" issue (see here) that seems like it's going to bite pretty much anyone migrating from v1 to v2.
For anyone who's interested, my new script is here. If I've made any obvious errors or missed important error checking, pointers are always welcome.
Thanks!