First off...

Is this an original engine in your car? Secondly, if original, what is your 2 letter block code?

Ram Air pans (first link) were ONLY for Ram Air cars. ALL 400 cars came with hoods with hood scoops. Only a handful (less than 500 Firebirds) out of 89,500 or so produced came with the upper ram air pan affixed to the lower side of hood and foam seal (as indicated by your first link). These cars came with a seperate hood scoop part number (open scoops) which was a different part number from the closed hood scoops which came on the other 10,400 400 manual and autos which ALL sported 400 hoods with CLOSED hood scoops.

The PROPER air cleaner with the proper carb if your car is a 400 is a 7028274 carb or a 7028275 carb.

The PROPER and CORRECT air cleaner for a 400 car WITHOUT Ram Air is

http://www.ebay.com/itm/1968-68-PONTIAC-...61d&vxp=mtr

http://www.ebay.com/itm/1968-gto-or-fire...720&vxp=mtr

Some sources say the base housing (in black with snorkel) is PP, some say PR.

Google is your friend...