72 demon defrost question

[mikes67]

So the story goes i have a 72 dodge demon at some point in its life someone stuffed a 73 an newer a/c and heater core in it, so during are restoration, we added the correct firewall piece,and a/c heater box to the car my question is how does the upper defrost duct connect, am i missing somthing with this box i purchased, i have a parts book and it is ver vage on the defrost duct and piping in help please.

 

[RedFish]

that plenum had a added piece, a goose neck of sorts that took a square opening at bottom and ended with 2 round openings at top ( square chested, 2 headed goose ? LOL )
Anyway, the piece was repoped a long time ago so there are plenty of them available today.

 

[mikes67]

That's what o need to find I looked and can see where it should be thanks