Okay, I've been thinking about your 56 and how it's a favorite writer as well as being a beauty. You have me worried for you now, because on further thought I think your concern as to whether replacing the feed could change its writing characteristics is a valid concern.

If you were only collecting and not using your pens, then it would be smart to change out the black feed for a correct one. But you know, when you're writing with a pen and enjoying 'that certain way' a favorite pen responds, and how you expect it to feel while writing, you maybe don't want to mess with that magic. Very favorite writers don't come along every day.