Ah, yes, there
it is.
Here's what happens when you follow the template literally:
Here's the same, with the bottom curving upward along a spline that crosses a 7° construction line about 2/3 of the way along its length.
The rear truncation is just slightly taller than a US license plate. Looks like you will have room on both sides for reverse lights and a license plate light.
Also, as you can see, I was a little sloppy where the tail attaches to the car, leaving a gap.
EDIT: I should add, this model is 4.89m long, 95cm longer than stock. That's much better than the 5.42m that I predicted in post #1 of this thread.