Do you still have the original stock? If so, that's what I'd use for the pattern. I'd use a wood blank slightly thicker than the final stock thickness, and then I'd bandsaw to the basic shape and then begin removing wood to work down to the final shape. Sounds easy, huh?
You did say it was a lever action, didn't you. I don't think I'd even try to make a full gunstock for a bolt action. That's just too darn much work.