I figured with it designed like this, I could save space on my grilling surface, since it only comes out 3" from the inside wall. I couldn't tell you it works better or worse than a the common 90* vent elbow.
I have a friend building me a diffuser plate and a basket, valleypoboy you say your diffuser plate didn't work! Did you make one with graduated holes that get larger away from the firebox? And did you cover up the top of the hole between the Firebox and cooking chamber to make the heat inlet smaller and force it down under the diffuser plate. Has anyone else used the copper high temp RTV and had problems like THOOD, I bought that kind but haven't used it yet, wondering if I should use the red/orange high temp, it says good to 600 degrees and the Copper is rated for 700 degrees so something doesn't make sense.
My diffuser right now is thin sheet steel approximately 16" x 12". I did bend it up on about a 45* angle for the last few inches and it sits perfect, meeting up with the right side wall of the CC just above the FB hole and just below the 2 bolts that hold the FB and CC together. It does not have any holes in it right now and left NO gap between it and the CC wall. It sits flush, but it is NOT bolted in.
I have nothing on mine right now for sealing the top lids. Mine has several areas where some smoke gets through, but I've been hesitant to seal it. I did a temporary seal on the side door of the FB... I just folded aluminum foil down to about a 2" to 3" wide strip and folded it over edge of the door all the way around then closed the door. It doesn't look great, but it sealed the heck out of the door and has stood up to 3 cooks so far. If I could find an adhesive that could take the heat, I could do the same for the 2 top doors, but keep it nearly invisible because I'd just be covering the inside lip.