The only nibs I've been able to find, Mike, are pretty straight. None of the ones I've seen have a shoulder that drops down to the threads as would be required to avoid the step down. I visited the nibs site one day and had a look around (http://www.nibs.com/). They show some commercial pen nibs that do have a shoulder (e.g., Schaeffer). You might be able to figure out a way to cut threads for one of those and adapt a kit if you have some metalworking equipment available.
