Andrew, if you are looking for body upgrade for the E53, you should look into Hamman, AC Schnitzer, Hartge body kits designed specifically for the E53... Manufacturing a kit for the E53 from scratch, basing it off an E70 body kits/style might not yield a desirable effect, and, as a matter of fact, may make your car look too funny to be considered a seriously luxury/performance contender on the road (even if the underpinnings are powerful)...
What i am saying is - go with proven looks instead of trying to create your own look... those designers that i mentioned, have whole departments that test the body kits before releasing them to public...
https://www.google.com/search?q=bmw+...w=1366&bih=667
https://www.google.com/search?q=bmw+...w=1366&bih=667
https://www.google.com/search?q=bmw+...w=1366&bih=667