For anyone else that is trying/wanting to do this.
My uncle and I did some looking around and testing and have figured something out. Looking at some Arduino to Lego shield program files, they seem to do more than just have nice plugs so that you don't have to chop up your wires to connect them. So instead of trying to reverse engineer them I am just going to buy a compass sensor. Reverse engineering the shield is probably not impossible, however I am just going to spend the money for a compass rater than hours/days/week/however-long-it-takes to do so.