Most brick ovens have a space beneath the oven floor that accommodates wood storage.
When I designed an oven for a colonial era house in New Hampshire, I incorporated genuine antique brick in the woodbox.
Since I was pouring a slab for the oven and I wanted the entire woodbox to be made of brick, I set antique bricks on the arch form, and filled the space above with concrete, reenforced with rebar. This effectively mortared the brick in the roof of the wood box with little effort.
In another oven, I used the same form to support the stones forming the arched face.
Note that arch forms need to be raised on shims that can be removed after pouring, allowing the form to drop and slide out.