I read through the Xvnc Terminal Server tutorial and made the suggested changes (except the port 177 part, I just enabled Xdmcp) and skipped steps 7-9. I figured I would just use vncserver to start with to get a remote session running then set up vnc as a service later.
Step 11 dumped me back at the command line so I ran startx and I ended up in 1980s display mode. I rebooted - bad move!
The machine IS rebooting, albeit very slowly because at every point it is 'waiting for xdm'.
Anyway, the vnc startup script was something like:
xsetroot -solid grey
xterm -geometry ???? "$VNCDESKTOP Desktop" &