Jeff, when I started researching gas deck ovens, I, too, was surprised by the simplicity of the heat deflection.
The flue is in the center back. I can't seem to find any parts list, but I'm guessing there's most likely a vent over the center ceiling bricks. I kind of doubt that this has Neapolitan oven style exhaust heat recycling.
While it is simple, I'm not so sure it would be that easy to incorporate in the LBE. I've been recommending thermal mass for the ceiling of the LBE for quite some time, and, so far, no one's really warmed up to the idea. Firebricks and 2" Fibrament are naturally diffusive, but Fibrament isn't sturdy enough in a high pressure burner setting and firebricks take a long time to pre-heat and are a hassle to cut. Chau went the firebrick route on one of his builds and I believe had fantastic results without any deflector in place. Still, it's a lot to expect for people to work with 1.25" - 2" hearths- and the hearth thickness/conductivity plays a big part in the mb. An mb wouldn't work with cordierite. As far as channeling the heat up the sides, into the oven chamber and then out the top of an LBE... I don't see how you could do it without some welding. A deflector under the stone with tall lips on two sides might work, but you'd still have to exhaust everything through the middle of ceiling.
Hmmm... if there was a 19" steel cake pan that you could put an 18" stone on (propped up a fraction of an inch for deflection). Then you could hang a 21" stone about 1" up from the cake pan, with a hole in the stone to vent gas.
Anyway, you get the point, translating the mb setup to an LBE- not as easy as you might think.