Which gas cap is correct??

[72peace]

I was looking for an original gas cap on my 69 custom but I've two different type caps with the same part number. Which one is correct or are both correct depending on some arbitrary assembly line supply house?

Here's the two I'm looking at, while the first has a smooth face the second has an indented ring in the center:

http://67-72chevytrucks.com/vboard/s...d.php?t=728703

and

http://67-72chevytrucks.com/vboard/s...d.php?t=727388

Both appear to be the correct number but look very different.

Help,
Nathan