a big Brisket can be forgiving, I'd not worry or maybe even go a little hot & if it's not finishing to your liking/timing you could still transfer it to the Caja (as backup oven)
(after some smoke & bark has developed, it won't pickup much flavor.)
How'd you marinate the Caja cook (pig?) I recommend MOJO marinade/injection, very acidic & delicious w/ pork