As a willing repeat participant in the 24 Hours of Lemons, I will indulge the OP.
First, the fat edge goes toward the front. Any other way makes you look like a tool to anyone who understands aero.
Second, as I'm post #19 and the only person to give you tech advise so far, plenty of people are going to see you as a tool anyways.
Now the tech advice, with safety stuff first:
If you mount it that far back and at that angle, you're going to lever your front tires up, losing steering control at highway speeds. To keep it neutral, you're going to have to mount it fairly flat front-to-back. If you want to put anything more than 2* of angle on it, mount it in front of the rear wheels. My race team had a moderately-sized rear wing on one of our race cars and we lost our front splitter halfway through a race. The front became significantly more squirrely. Aero done wrong is no joke.
The more angle, the stronger your mounts will need to be. If that thing rips off and goes through a windshield, you're going to the penitentiary for involuntary manslaughter. Backyard jungle-gym braces aren't going to cut it. You will want to weld four 4"x6" steel plates to the bed sills, fully weld two 1.5"x3/16" angle iron tabs to each plate, and use circle track radius rods and heim joints for your arms - that'll make the angle adjustable.
There are probably ways to mount it on the cab, but I wouldn't do it. It's going to bend and warp your roof. The Our Lady of Perpetual Downforce racing team actually has their Cessna wing welded to their roll cage.
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