Pretty accurate......(spoiler for those that have not seen the ending)....

After watching the movie, wanting to know how accurate it was, I read the final portion of Go Down Together and found the pursuit was pretty accurate.

The set up of the tireless vehicle and the father was accurate.

In the book though, it portrays one of the others as starting the shooting of Bonnie and Clyde (not the Kevin Costner character) before Costner gave the go ahead. Though in the book the Hamer (Costner) is described as brutally putting down the finishing shots into the vehicle.

The book also reveals a local sheriff was tasked with notifying J. Edgar Hoover's people first, however, because he could not reach the one agent by telephone, he notified Hamer of Parker and Barrow's upcoming trip to the Louisiana family of their cohort.