Here is a pic of our new bike. It is not quite how I would of done it if I started from scratch, but it saved a bit of time by utilising an old funny bike frame I had.
The main thing is to see if it works with this configuration and the subsequent lightly loaded front wheel. It definitely isn't for using with a heavy stoker.
Only been up and down the road a few times so far. Didn't fall off which is good, but it does feel a bit different.