1. My Sport Coupe had a split lock washer on that screw when we got in 1962 ... it never shorted.
I could be wrong but as I remember the lock washer was captive on that screw.
Screw had rolled threads only on the bottom 1/3 of screw so washer would not fall off.
Not sure they had this setup originally.
I think that screw is still on the horn.
2. I see that Bratton's kit has a washer included according to the photo.
I wonder if they short if washer is installed?
https://www.brattons.com/pro-pack-sp...build-kit.html
UPDATE:
I guess that I remembered wrong ... no captive but does have shoulder threads and thin lock washer.
PHOTO of screw ...