Just saw this ad for the largest gamebook ever; over 1200 pages and 19 endings. An actual printed gamebook, which I've not seen many of lately; and looks like it comes with a set of stickers to keep track of your attributes, which is an interesting way to do it, as well as a map and character sheet.

Might be fun to do it old-school.

https://www.kickstarter.com/projects/itbboardgames/alba-an-open-world-adventure-book

Whoa!

I find some old CYOAs at used book stores around here from time to time, but they are generally around 50 pages or so (I believe).

This seems like something I'd start and never finish, but it is interesting.