One thing I noted, though: the angle iron really belongs in with the firebrick, not out with the veneer. You essentially have nothing except mortar supporting the brick over the oven opening, and another of those pesky joint lines lined up with the side of the opening.
Before you apply veneer, I’d strongly recommend you take your angle grinder, cut notches into the horizontal mortar under the first row of upper brick, and place the angle iron in there. You want about 4 to six inches on each side (a total of 8 to 12 inches wider than the opening).
Place the angle iron so that the upright portion is inside the oven. This will maintain a flat surface for your veneer.
“Why” is a perfectly reasonable question, by the way. The “because” is that while the closure looks like an arch (which is what is behind that opening), it is a simple wall. Those four brick right over the opening have the weight of the remaining four or five rows pressing down on them. Unless you reinforce them, my prediction is that the two rightward vertical joints will slowly fail, then tumble into the mouth and take the veneer with them. At the very least cracks will develop in the veneer as the wall behind starts to sag.
You’ve come this far—this is going to be the best-tasting pizza EVER when you are done.
Or it was clearly me who was misunderstanding! So sorry.
Yes, that is where it is supposed to be, and I now have an archived response for someone who actually left that step out. I apologize.
Now to your actual question…
I would not apply the veneer inside the mouth of the opening, just the face. It will look nicer to leave exposed firebrick there. The veneer won’t stand up to the radiant heat coming from your oven, and in particular the angle iron will absorb that heat very quickly.
Better to leave the “blue” areas exposed.
Of course my opinion on how good that pizza is going to taste has not changed!