The book is based on a work of fiction, a screenplay especially written to be a movie. On the DVD William Friedkin, the director said it was very loosely based on some things Tom Brown had done. Like tracking people for the police. That's where it ends.
Tom Brown said in "Blade Magazine",
"The knife you see in the movie was made by my friend Dave Beck".
The same article says that the actors handled the original like it was gold.
The knife in the pictures above was made by Dave Beck, it's one of his early models with the hollow ground draw knife edge. Dave doesn't make them like this anymore, he flat grinds the draw knife portion. The knife in the film also features Dave's "pearl grey" high polish blued finish, and buffed black linen Micarta handles. You can also see the sawteeth that he machines on the knife with his vertical mill, which are unlike any other teeth seen on a knife.
The prop department made dozens of sloppy looking (rubber and aluminum)copies of Dave's knife for various scenes in the film, (not close ups)like the scene where they forge the blade and file on it in a vise. And of course the knife fight scenes used aluminum and rubber versions cast from Dave Beck's original. The DVD shows a table full of the prop knives.