careful!!!!
Yeah, you can buy the wrench easy enough, but there's still a good chance you'll torque the action bars trying to get the nut off, and if you do,...the pump action will bind and the gun is pooched.
Look in Brownells catalog for new forend metal. If you're setting up a turkey gun of a tac shotgun, new metal is not that bad price wise, especially if you get the matte or parkerized finish, and you'll be ahead in the long run.