Exactly as he said the only resemblance between the two engines is the name Zetec but this is where the similarity ends. You currently have a Zetec-SE (Sigma) where as the engine you are looking at is a Zetec-E, as said they are totally different, the inlet and exhaust are on opposing sides to start off with, it's easier just to buy a 2.0 outright and use this as your base.

Martin