72 GMC A/C Help

[jeremyluke]

I'm putting factory air parts back into a truck that a previous owner stripped out. I bought the center air vent, gasket, and plastic Y duct that goes behind the dash however I am unclear as to how the pieces attach to each other. If someone could enlighten me as to how they attach or if there is a specific piece of hardware I need it would be greatly appreciated. I've searched parts catalogs from multiple companies but no one seems to sell parts for or even understand how they connect. Golden State, Brothers, & LMC all need to implement tech support.