The engine code is the 8th digit of the VIN and, as mentioned before, should be a 7 for an '86-'87 intercooled turbo car or a 9 for '84-'85 turbo (non-intercooled). Unfortunatly, there is nothing in the VIN that seperates a GN from the other variations. Only the trunk sticker will tell you if it's a GN (WE2 code as mentioned before) but check that the VIN on the sticker matches the vin of your car. If not, the trunk lid is from another car.
Does anyone know if our cars have build sheets hidden in the car somewhere?