Kitanohara Noriyuki (Ep 19 episode director), Ishidate Taiichi (Ep 20 episode director), and Yamaguchi Mayumi (production manager?).
The storyboard for this scene was drawn by Sakamoto, who apparently said that he really wanted to depict two guys having a back-to-back conversation. Yamaguchi-san commented that it shows how close they are as friends - but also noted that it'd be really strange for them to be talking face-to-face.
It's also rather interesting to watch Akio's cigarette: whether it floats when he talks, or is stuck in his mouth depends on the person who did the key frames. And sometimes, it's even forgotten by the artists, so the episode directors have to go and add it
The enunciation (tongue twisters) practice at the beginning - some of the seiyuu had done that too! (Btw, that passage is from "Uirou uri" or "The Medicine Seller", a Kabuki play which is supposedly "little more than a chance for the actor to display his elocutionary skills".)
The hands are all different (Ueno-san made sure of that) - I thought that was pretty cool too, when I first watched the episode.
The animator responsible for the key frames here apparently based it on real photos. They really need to do proper research.
Ishihara-san wrote the contents of that open diary page. I think you should be able to read it on the Blu-ray version. Super-detailed, huh?
Sakamoto-san, who did the storyboard for the ending, actually listened to that dango song over 400 times! He'd wanted to colour it with crayons (or in crayon-style), but wondered how the finished product would look.
and er...that's it for CLANNAD - the last volume's commentaries were either boring, or I just wasn't paying much attention at all... After Story's up next.