Well, if Adam were formed from the dust of the earth and Eve were formed from his rib, neither would have been attached to an umbilical cord at any point in time.
Afaik ribs don’t come with umbilical cords (with coleslaw or BBQ sauce maybe, but never heard of ribs with umbilical cord).
So, in this hypothetical Q and scenario, a belly button for either would hardly make much sense, would it now?