Just a quick update - I've got a Zap channel connected with a Hubzilla/Red channel over Zot6. I haven't started posting anything yet (this is certain to take a few more days to sort out the conflicts), but they're friends. They've discovered each other and assigned permissions to each other and received and stored them successfully. The cryptography is working.
It's Friday night here. The beer is cold. It took a lot of work to get to this point. For right now I'm going to quit while I'm ahead and savour the moment.