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Jon - Mike V in post #9 is pointing you in a good direction.
Very often folks new to Model A's will fill the radiator to the top and experience water pushing out when they are driving. This is normal as the radiator will push water out until it finds a level that it likes. As long as the tubes / core is covered you will be fine.
If you keep adding water back to the top you will always have water pushing out.

Get a inexpensive meat thermometer and manually check your water temperature on a regular basis until you learn what the temperatures run in your car.

One other thing that can cause water to push out of your radiator is compression leaking into the cooling system by a bad head gasket or a head that is not torqued down properly to 55 lbs. Usually you will notice this more under heavy acceleration up a hill.