Dear Joe,

The best I can do is offer you a page we have on our “Where do I write?” Vatican web page:

• Where do I write? — Vatican Mailing Addresses
• When writing the Pope, what is the proper way to conclude my letter with the enclosed questions?
  

There was one web site that went into detail on a similar question as your, but it no longer exists.
This one may help, since most of the time, most any bishop could become a pope.

• How to Address the Pope

I remember one of the keys when writing your letter was: being short and to the point.

That’s the best I can do. Maybe my colleagues have some ideas.

Mike