The number should be stamped into the top bar of the radiator support, between the radiator and th battery. It was generally covered by a sticker giving information on the antifreeze. If you were standing in front of the radiator the sticker would be just to your right. Have seen cases where an owner has removed the sticker and filled in the stamping before repainting the car.
If you place a mirror just below the upper radiator support facing up you should be able to see the numbers. One person who filled in the numbers on the top side left the bottom untouched. Thus you could still see the numbers on the underside.