The defrost vents were missing when I bought my truck, an '89 379.
I couldn't find a reference for what was supposed to fit so I took a chance and ordered two of these:
Red Dot-Red Dot Louver Defrost Outlet Fixed Vane 11/8 in. x 81/2 in. - 72R3000 / RD-5-6017-0P-72R3000
They fit the hole in the dash and the ducts perfectly. I'm just not sure what is supposed to hold it all together. The dash vents snap in, these don't and don't have any screw holes.
Is there some kind of clip that I'm missing to hold them in?