This the process and end result.
The functional vents started out as new oem vents which I cut out, painted and backed with black wire mesh.
The fender cuts were done with a CBN wheel on a dremel (link
here). This wheel works fine as long as you go slowly and guard against the dremel's chuck touching the bodywork.
I used two layers of tape holding a plastic ruler along the bottom of the vents. If you do this, try to keep intact the receptacle for the rear-most press clip; it helps align the new piece.
After cutting the fenders, I put two coats of flat black on the edges of the cuts to minimize potential rust. I also blacked out the inner body panel just behind the vent, which was still showing a lot of primer ( see 2nd photo.)
Attachment 145935
FYI The 'supercharged' sticker is from ebay. I wanted some subtle bling.