1969 Dodge Dart GTS - Drain Radiator To Remove Heater Box?

The service manual says to drain the radiator before removing the two hoses to the firewall connectors to the heater box. Is this really necessary? Any other tips to easily get the heater box out and rebuild? I’ve heard remove the seat and glove box and get the Detroit Muscle rebuild kit. Mopar A Body 67-72 BIG NON AC Heater Box Rebuild Restoration Seal Gasket Kit