55.2-59 Where do the defrost ducts go in the dash?

[yossarian19]

This seems like a silly question to me but I just don't see any factory provision for a defroster duct. Is this a hole saw job or am I missing something right in front of me or what?
The truck is finally decent enough to use on a daily basis but man, I'm getting tired of wiping the fog off the glass with a rag!
Need to put a heater box & defrost in this thing soon.