Heater core bypass

[My77Vette]

1977 Corvette without factory air.... I am looking for a bypass valve and soul like to know the size I need to purchase. I am not in town so I don't have access to the car and while away I woul like to purchase the right size valve. I see options for 1/2". 3/4" and 5/8" hose connections. Can anyone tell me the fit? Thanks