You should read the book, because the screenplay is going to be completely different I'd stake a lot on it. The book honestly reads fairly dry, although filled with what generally feels like accurate to semi-accurate information throughout. There are some very bold claims that also seem as thought they could be true but, would be historic if they were. That being said none of it jumps off the page (i.e. Nick Pileggi's Wiseguy is the Goodfellas screenplay nearly copied) this will all be reworked to be told better than the book conveys it. They book tells a very dull but potentially accurate detail of how Hoffa died and who participated doing the same with the Joe Gallo murder. I doubt the movie will combo over that as calmly as the book did.