I've measured it out and its 6 or 7 bricks up to the gas element, the 4 bricks for the opening to the dutch oven, then a lintel across the opening and 2 bricks to the bottom of the oven door

Its certainly not going to look as clean cut as this, my oven is thinner but taller and I intend to put a metal front on it.... unless I can find some heatproof glass !
the oven i have has the internal glass section of the door but the outside glass isn't there, must be why they were throwing it out??? it would be quit cool to look inside but as i have guttered the oven i'll have to install a light myself.
I'll just drill some holes in the top of the dutch, this will help the wood heat up whilst allowing the smoke to exit.