Further to the last post you can see i have cut a brick to fit into that angle slot, 2 whole bricks will go infornt of it to complete the oven seal.
heres the mock up of what i intend to do, i feel it is important at this stage that you know where your chimney is going to go and HOW you expect to level off that angle. this is a great website with good images http://www.villagok.dk/brickoven/july2005/july2005.html , scroll down to the image of his "drop"
I happen to have picked up for free some already cut angle bricks so i am using them.
the inside after its all closed up (not cleaned) but you can see how that simple side arch with 2 bricks in fornt makes a good seal, the IMPORTANT thing for me has always been not to have areas that can hold ash and then eventually drop into your food, this design i think achieves that.