Like Matt said, cinder block is dimensional and every block is almost perfectly identical. I ordered 6 or 7 extra in case a few were chipped or whatever and I did end up finding a few that has excess material and caused a 3/16" difference here and there but when I swapped them out, I ended up with a near perfect base. Also keep in mind you’ll be putting a thick layer of mortar on top of the blocks to lay the hearth on, so you’ll have that to even things out if need be. Mortaring block is nowhere near as easy as YouTube videos make it look. It’s definitely an art that you won’t pick up until your last few blocks when it’s too late.
I’m also using SBC on my dry stacked base. I opted to build the hearth and oven first though, just in case those ~2,000 lbs of material caused any compression on the bricks, I wouldn’t end up with a crack in the SBC. Right now I’m waiting for the oven to cure and then I’ll SBC the base while doing the stucco shell.
Lastly, stucco and SBC are essentially the same. Fiber reinforced mortar. You can interchange them. I’m actually convinced they’re identical and prices differently due to marketing.
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