Recommend you check out all the info on the Weber Virtual Bullet site. There is an entire section dedicated to building a mini WSM. Reading through it will save you a lot of time with.trial and error. I love mine and use it a lot more than I thought I would when I built it.
WSM, 99 & 09 Performers, 2-OTG, SJG mini WSM, Summit 420, Q100, Akorn, and Schwenkgrill