I very much want this to the be the right lens because, if it is, we're that much closer to having an accurate HAL replica. But allow me to play Devil's Advocate here and point out that neither of the references above say anything about the Kenko being the lens used in the HAL panel. Though the references on Underman's site do name the lens clearly ("Kenko 0.16x No48221"), they don't tell us how the lens was used. We are merely told that this is the "actual fish-eye lens used for some of the HAL shots." That's a fairly vague statement.
In fact, if we examine the wording of Underman's text closely, we find no indication at all that this is the lens used in the HAL panel (physical resemblances between the lenses notwithstanding), but instead a strong suggestion that the Kenko 0.16x No48221 was a lens (perhaps not the only one) used to shoot HAL's POV shots:
(1) According to Underman, information about the Kenko came via Gavin Alcott, son of the late John Alcott, who was responsible for "additional photography" (as opposed to set design or visual design). In other words, this lens was used by a cinematographer for shooting. It wasn't necessarily also used by a visual designer as part of HAL's physical construction.
(2) The particular wording of the reference to the Kenko ("actual fish-eye lens used for some of the HAL shots," italics mine) suggests that other lenses were also used. Again, this supports the interpretation that the Kenko was used as a practical shooting lens (and may or may not also have been the lens used in the HAL panel).
(3) The heading above the text ("How does the world look to HAL?") once again indicates that the author is writing about the way in which HAL's POV shots were accomplished, not about the lens used in the construction of the screen-used HAL panels.
Again, I'd very much like to believe that the Kenko is the lens we see when we're looking at HAL. And I'm not saying that it's not. It sure looks like the right one. But I think the reference in the site above does not specifically support that interpretation. It suggests only that the Kenko was used as a shooting lens, without addressing the question of whether the Kenko was part of the HAL panel.
2 cents