I doubt the new reservoir is the same and you can get one for a Taurus at a salvage yard. Before I went to a lot of trouble I'd try that, replace the new one with a real Tarus tank and 16 lb cap in good condition. The coolant should be the color of the anti freze but not muddy and that calls for a cooling system and heater core flush. Overheating is the number one cause of blown head gaskets so get it fixed pronto. Boil over: You must have a 16 lb reservoir cap or the cooling system will not work the way Ford designed it.
http://www.aa1car.com/library/overheat.htm