OK, squat in front of your 300E with a tape measure. Find a straight stick or pole and hold it straight up against the bumper, (on the side of the car) I positioned my stick against the top of the bumper which also happened to be the upper rear most part.

Next I put the tape measure between the top of quarter panel and hood. Going straight out and measuring to the stick, I get the 7 3/4 inches. That should give you an idea of how far out the flares go.

Are you sure this is going to work, I have never seen this done to another 300E/400E?