Attachment 17278Great project Hersbird. I think you are going along the right lines there... slight curve, round 10 degrees with a sharp ending. Use the start of the existing curve to begin the roof line panel. And keep it lightweight as possible.
As for the front i like your ductwork idea, but maybe bigger duct, softening that sharp corner, using similar frame to the back but smaller, 8 " radius. ... OR! ... a turning vane over the sharp edge like 'cab over' semis have
See attached quick and dirty sketch, sometimes its just easier to draw it!