If I play Stirring Grave while I have both pieces of a Gigantic creature in my discard pile, can I target it and archive both pieces?

Stirring Grave specifically targets a creature, not a card. If both pieces are there does it count as 1 creature?

Stirring Grave's ability says, "Archive a creature from your discard pile.".

Gigantic creatures count as 2 cards while out of play, each with the same title, house, and card type. That means that when a gigantic creature such as Niffle Kong is out of play, it counts as two creatures. So Stirring Grave can only archive one half of a gigantic creature.