I think i've worked out what to do with supporting the oven on bricks.
I will create the side brick walls VERY close to the ovens sides, then when i get to the correct height I will turn bricks around/sideways to create a shelf for the oven to sit on, the weight of the bricks above forcing down on the sideways bricks will keep it stable, if i do 2 layers of bricks intersecting then the weight of the oven + food will be spread over a large area, I think i will also include a piece of reo across the void at the back .
because the oven i have has a draw under the oven door of @ 20cm i will be taking this out and the frame will be left, i'm going to cut the front bottom piece off so its open for the dutchoven and thus the oven will be supported by the side-frames. THUS this sideways brick idea will happen 2 bricks up the element area. (the element will still need to be supported by a brick platform
this method will save a few bricks (@ 32+ eg: [8x4] for the 4 corners) and it will allow for extra side ventilation.