any time
Harrison Radiator made rads and heater cores for GM until GM bought the company and made it a division, part of Delco I believe - the heaters were assembled wherever that division was [originally NY}, then GM installed whichever model heater was required on the assembly line as they were always special order, or they were sold/installed at dealers
you have one of 3 styles, factory installed standard, or deluxe, and dealer installed 'basic' .... find some
heater info pics here, and installation
info here for the 2 models of factory heaters, standard and deluxe
Bill
