How do you remove the heater core on a 57 Chevy?

Drain the coolant. Remove heater blower motor assembly...disconnect wire. Remove hoses from the heater core. Remove the 2 vertical metal "keepers" from each side of the heater core duct by prying them upwards. Also...there might be some screws through the firewall interfering with the metal "keepers" so be sure to check and remove them from inside the vehicle. Carefully remove the duct...it might be stuck with some kind of sealer or gasket. Once the core is exposed remove the screws that hold it to the fire wall and carefully remove it from the car. Installation is pretty much the reverse. Take your time and it should go easy. Oh...check the heater box for straw, hornets nest's and other foreign materials.