Check to determine the length of the bumpers. If they are 60", they are Model T and not correct for your car. This was a common mistake made by many owners of early cars that thought they should be open end. There are two different versions of open end early rear bumperettes. These are almost impossible to find now and have to made from closed end units.
Also, I've seen dated photos from Nov 1927 showing early cars with closed end bumpers. Brent is correct in asking the number. Unless you have a three digit engine, I would recommend putting closed end bumpers on the car.