Text Dataset Help: Need to figure out how to get the publication date of a text
I would hazard a guess that most books uploaded on Gutenberg also have a Wikipedia page. Especially the well-known books. There are a few Wikipedia related Python packages (i.e. Wikipedia) that can make it very easy to search for the title of the book, navigate to the book's page, and extract the publication date. An optimal example might be Alice's Adventures in Wonderland. It'd be trivial to extract the date from that page, which appears neatly in the info box, and convert it to a machine readable format in Python.

Or, you could attempt to scrape the info straight from Gutenberg. Perhaps consider Selenium, although make sure you limit your bot's rate so you don't adversely effect the site.

Lastly, trying to predict the publication date might be similar to predicting the author; both may be derived from writing style. There's a lot of work on this topic, a Google search or an arxiv search will help. Here's one of the first articles I opened.