Here's a mod I did to my New Braunfels Super Longhorn Deluxe smoker.
Klose BBQ Pits in Houston custom made me a charcoal basket to precisely fit my firebox. Since the NB firebox is round, we were careful with the dimensions to allow the basket to slide in the side door (without having to lift a hot basket through the main top door). With the round box, and the square/flat basket, airflow is well managed and the height is perfect.
Klose did an awesome job at a reasonable price and were very accommodating. I highly recommend them for any smoker/grilling/fabrication needs.
Final dimensions are 12" deep by 17" long by 8" tall.