Since your new to the scene it sounds like you could use a little bit more info about identifying heads, just so you can be sure what you're really looking at.
Here is a pic that will show you where the relevant numbers are on Pontiac heads. Other numbers on the heads than what are circled in this pic don't mean anything as far as identification goes. As you can see, this is a 6X head.
Not all heads have the secondary stamping. To the best of my knowledge, heads that have a secondary stamping due to various chamber and/or valve sizes used with the same basic casting are 4X, 5C, and 6X. Again, this is a picture of a 6X-4 head because it has a '4' as the secondary stamping. The 6X-4 variety had a smaller combustion chamber than the 6X-8 or the rare 6X-6.
Finally, all Pontiac factory heads are D-port except '68 RAII , '69 - '70 RAIV, '71 - '72 455HO, and '73 - '74 455SD.
Hope that helps and welcome to the Pontiac hobby!