You can already do that on Wikisource. For example, here's p. 658 from the entry on "Molecule":
https://en.wikisource.org/wiki/Page:EB1911_-_Volume_18.djvu/...
Also OP: I noticed some fidelity issues in your version (at https://britannica11.org/article/18-0684-s2/molecule). For example parts of the math formula under the line that ends with "the molecules of other kinds" ([1]) are missing (compare [2]). Also, in your version fn. 1 of this article is attached to "as they have always done" ([3]) but it should actually be attached to "Atom" on p. 654 ([4]):
[1] https://britannica11.org/article/18-0684-s2/molecule#:~:text...
[2] https://en.wikisource.org/wiki/Page:EB1911_-_Volume_18.djvu/...
[3] https://britannica11.org/article/18-0684-s2/molecule#:~:text...
[4] https://en.wikisource.org/wiki/Page:EB1911_-_Volume_18.djvu/...
As an example flow (since it took a minute to figure out): we can start at https://en.wikisource.org/wiki/1911_Encyclopædia_Britannica then click to navigate/browse volume > section > topic to get to a text page, then click Source tab, then click a Page Number (maybe hunt around for the correct page number), and see the parallel view, text + image. With previous and next page buttons available, retaining the parallel text + image view.
That’s a great suggestion. A side-by-side text + page view would be very nice for exactly the reasons you mention (verifying the text and seeing the original layout). I haven’t built that yet, but I’ve considered it.
Also helpful to hear that the links to the scans weren’t immediately obvious — I should probably make them a bit clearer. This may also not be obvious, but you can click the vol:page links in the left margin and go directly to the scan of whatever page you're reading.
Thanks again.