I would likely call for a Persuasion (or Suasion) test and FoRK Calligraphy or Writing to persuade the head of the order.
A linked Ob2 Calligraphy test to the (Per)Suasion test could also be what happens.
However - for the most part, creating the letter isn’t the task - persuading the head of the order is the task, and the Intent is to get an order of Knights. Unless having the letter be legible was important, I would simply say Yes to the Calligraphy test.