Here’s the ONLY reference with a sample I have found: https://help.datica.com/hc/en-us/articles/115005906626--Legacy-VPN-Client-Setup (scroll down to the Ubuntu section where it gives an example of charon-cmd syntax)
I still haven’t successfully gotten past the phase1 proposal even using the syntax noted there with the crypto parameters I got from ike-scan.
Edit: apparently charon-cmd (CLI tool associated with, but not identical to, the mighty waterfowl) is not sufficient. It supports m*** m*** so it gets slightly further than vpnc, but doesn’t support the right profiles.