One correction:
The TOP of front left (drivers side) cable goes to the rear of the right (passengers side) box.
You're correct that bottom control (RED) from the dash slider goes to the bottom front of the left (drivers side)
Just mocked up the whole system on the bench to figure how to do the routing
Barefoot

delete

I just installed my fresh air box. I followed Ian Karr's advice and wrapper the grommet and screen with rubber bands to keep it in place. The left side bolt wasn't too difficult to get in but the right was a real challenge.

I placed a 2x4 under the fan and slid in 1/4 slats to wedge the unit up and put a spreader bar against the divider wall to push the unit towards the rear.,

Click to view attachment

One interesting complication was that my fresh air box wasn't square. I had to wedge a dowel inside the box, at exactly the right length to force the corners to be 90 degrees. I'm going to let the box remain in the car for several months to see if the summer heat can bake the box back into being square and then remove the dowel.

George