Take a look at these. I used them in my build and the work pretty good.
FYI, I need to add a third damper to my firebox, I'm getting limited flow for higher temp cooks and need to crack the door.
This guy's website has quite a bit of stuff, shipped fast & cheap. I was happy with his customer service.
Weber 26.75 OTG w/CI grates & SJ/WSM Mini
Home built 24"x72" reverse flow stick burner trailer with 18"x44" grill w/CI grates and upright SS gas oven/smoker.
Home built 48" fire pit with a 30"x30" Santa Maria style ranch grill.
Home built lump charcoal retort, iGrill & a bunch of other cooking toys.