There were no Plantagenets until 1154, when Henry FitzEmpress, son of Geoffrey Plantagenet and Matilda of Normandy, took the throne of England as a cadet of the House of Anjou (the other branch became kings of Jerusalem). And by then, Matilda was long gone and her realm was a bunch of city-states.
During Matilda's time, the head of that house was Geoffrey II, Count of Anjou, who died in 1060 and was succeeded by his sister's sons, who were busy fighting the House of Rollo, the King, and each other.
A better PoD would be later Plantagenets marrying into the Sicilian House of Hauteville.