Need help installing factory A/C in a non-factory A/C 67-72 Truck

[kna4977]

There has to be someone else out there that has had the same idea as me, installing factory air in a non factory air 67-72 Chevy or GMC truck. With that being said, I would appreciate any tips that you can give me, that would make this installation easier and more successful. I am especially worried about drilling holes in my dash for the vents. What is the best way to do this? Also, what is the best way to cut out the firewall, and what is required to install the flapper that closes off or lets in outside air? What is the best way to wire in the factory air unit into the existing wiring harness, or is it better to use the wiring harness from the factory air truck? I'm sure I'll have more questions, and there are probably questions that I don't even know to ask at this point as I just have all the components, and have not begun the installation yet. I just want to know what I'm in for before I do it.