So, with about 10 mins of reading and 1 min of work, this site is now available with both IPv4 and IPv6. Thanks Bytemark for making it so easy, and of course to all the software stack that just works. If you want to test and ensure you’re using just IPv6, you can browse to ipv6.james.rcpt.to, which I have only published a AAAA address for.
Next up; update my Log3NF Apache module to understand IPv6 addresses as well as the IPv4 if currently does.