So Pluto is just a remake of these episodes of Astro Boy? (Spoilers)

And I've said it here before but it's more technically based on Osamu Tezuka's manga. The 1980s anime cuts an important part from the story that ends up being fairly huge in Pluto (with Urasawa's own original spin to be sure, but completely absent in that), the 2003 anime also rewrote it to fit in with the overall storyline they wanted for that series (I don't know about the 1960s one, and that part didn't make it to the US version which didn't get all the episodes). This isn't purism or nostalgia as there are things I like about both that Pluto didn't go with, just saying I felt Pluto was more inspired by that, and considering Urasawa's fondness for the manga it and that it's considered a tribute it makes sense.

That said, there do seem to be some nods to the anime, e.g. the 2003 one replaces a male character with a girl who is just made into a pretty boy in Pluto, heh.

If you want to check that out (edit: the Astro Boy manga) it's available on some library digital services like Hoopla and ComicsPus. It's Volume 3 in the Dark Horse edition, not even 200 pages. Plus there's a neat couple of pages by Osamu Tezuka describing what his aims of the story were. If you come across the omnibus edition it's in volume 1 of that.