Danny:
The factory heater core for the '64-'66 Chevy trucks has the inlet and outlet on the top of the heater core and they come out on the passenger side of the heater box through the top of the heater box cover. The heater core is held in place by two U-shaped strapes that are held in place by two 1/4" sheet metal screws. The heater core/heater box may be slightly different on the '60-'63.
I hope this helps.
Tony
