My 63 has the non deluxe heater, 2 lines go inside the cab, and I believe the 64+ had the "deluxe" heater standard. Look like the previous owner has installed the deluxe heater and done you a favor!
Here is the full '64 wiring diagram
http://67-72chevytrucks.com/vboard/s...d.php?t=193429
Let me know if I can give any more help...