Hi Greg;Welcome to the forum.The below link is one solution. Just make sure the brisket doesn't touch the sides or back of the cabinet.Brisket Too Large?Other options; if it is not too much longer than the rack, you can cut off a piece of the thin end of the flat. You use the cut off piece as stew meat, or if you have a grinder you can add that too some chuck, for hamburger or meatloaf. As mentioned in the link above, some have separated the point from the flat, and cooked them on different racks, with the point above the flat.
The link did not work for me. What did they do?
Make certain that your brisket does not come in contact with the side or back walls of the tower. If it does, it greatly increases the risk of a grease fire.