Tim,
The screw is likely in place to lock everything down once installed and adjusted.
No screw used on mine. Just a simple dimple that swaged the whole in in place. A drill and a 3/16 drill make short work of it. I suspect I could tap and put a screw in to insure no rotation.
For the wiring, I had to cut and splice the new ones in place after the lamp was mounted. Used shrink tubing to keep it all neat and tidy.
I did notice the anti-rotaion tab was bent a bit, so fixed it with a quick re-strike.
Overall, the job took 1.5 hours at a very leisurely pace. Being a mechanical engineer, I enjoy servicing and modifying my cars.
You might consider grinding out the old rivet from the inside and replacing it. A cherry rivet should do a great job albeit not esthetically perfect.
