You only get the effects listed in the item's description regardless of what spells went into its creation. The mighty arms graft requires bull's strength to make, but that spell is used up during the construction of the item; the bull's strength bonus doesn't carry over as a property of the item.
Additionally, the mighty arms graft doesn't explicitly let you use warforged components. Components can only be used by warforged, and the graft doesn't change what you are. Given that they can be made from arms taken from a warforged, though, I don't think it's too much of a stretch to houserule it so.
