Chad, you're exactly right. It was the A-17. I would never have remembered that it was Claude Mac(?) that did it but I remember clearly that he did use ink.
In the Frank Tiano article they used a jig made up from a square with a pencil attached. They stood the Mustang on it's nose, maybe on a Lazy Susan, sans spinner, and rotated the plane with the pencil in contact with the cowl. The square had a ruler along the edge so they could move the pencil up any given distance for the next line.