I've read that novel, and it's still extremely graphic to be toned down to a PG-13 movie.
The other problem with adapting that novel alone is that you really don't have Logan as a character...he's catatonic for most of the book, except for the flashback sequences, which basically end the same way the Weapon X story ends, with Logan going nuts and killing everyone. A movie needs to be more story than that.
There's another novel out called Lifeblood, which flashes back to WWII, and in that you see Logan using his bone claws several times.