Now i'm not associated with gutenberg in any form, but they do have a page for offline consumption:

https://www.gutenberg.org/ebooks/offline_catalogs.html

Perhaps you can find the information you are looking for there.

However if you plan on scraping or otherwise hitting them with a ton of traffic, consider at least to donate a good amount for the traffic you cause them. It ain't free after all.

Donations are always appreciated ;)

Presumably if you paid them enough money they would give you the books without you having to pay to scrape at all?