I did the inventory of the cement blocks I got so far and modified my paper plan accordingly. I have much more block 8X10X16 so the oven hearth floor will be slightly smaller than the Alan Scott plan, but it's ok. I laided the blocks to see if it all made sense and I think it will look good. I just made a slight modification to use the 8X8X16 block for the center pilar instead of the corners. The metal wash bassin will be the ash recipient and it's there to make sure the front opening is large enough to access under the oven easily.
In the meantime, I was able to acquire an old cement mixer: that will save me a lot of elbow grease! I will retake all the measurements, redo the mock-up and hopefully start the actually work soon!