What is the silver thing in the center of this picture, stamped "882"? I don't have that on my car. http://www.flickr.com/photos/robsalbum/2476405876/

 

That is where the gas tank vent tubes ventilate themselves... no spark or open flame please

 

As the (most likely) "other Rob" said, it is the gas tank vent system.
The '72 uses a charcoal cannister and a non-vented gas cap. Two or three gas tank vents go into the silver part in question and a main vent goes to the charcoal can. This part in question also helps separate fuel vapor from any liquid.
If a strong fuel smell is experienced inside the car, this "vapor separator" should be checked.

Your 70 probably does not use the charcoal can and may still use the simple vented gas cap.

 

I was wondering if that's what it was. It almost looks like it vents right into the interior of the car?????? Interesting.