After work today I got out all the parts bins and went through each bag one by one looking for the four screws for the air inlet.
I found them! And what they were labeled even made sense, although it wasn't "air inlet".
I gave the screws a quick cleaning and then a bath in WD-40. I purchased three denture containers to use the trays to seperate parts. The trays have openings in the bottoms that allow the WD-40 to drain out. The denture trays are the right size and I am not sure I could have found anything else less expensive. (They were only $2 each.) I used small colored zip ties to color code them. This will come in very handy when I have multiple batches of hardware. They also serve as a handle for pulling the trays out.
With the hardware cleaned up I made quick work of installing the air inlet.
I decided to finish securing the interior heater box to the firewall and to the blower housing. I started by tightening the exterior screws on the blower housing (we had loosened them to get the air inlet in).
I located the hardware needed to secure the bottom of the heater box. The screw on the left secures the heater box to a nut in the firewall. The screw on the right secures the heater box to a receiving nut on the blower housing.
I cleaned the two screws up, as well as the hardware for mounting the blower motor to the housing.
First screw is in.
The second screw stripped out the front portion of the fiberglass receiving nut on the blower housing. It was either this way from when it was removed, or because of our added firewall padding it is now thicker and the screw is not turning as far into the receiving nut as it did before. You can actually see the fiberglass powder on the firewall directly below the receiving nut in this picture. Since the receiving nut already had a hole all the way through, I threaded a bolt from the outside through the firewall into the interior. This way I am still using the receiving nut, but it should end up being much stronger, and I won't have to worry about it stripping out.
I used the machine screw on the left to retap the receiving nut. However, it is not long enough to reach all the way through. I will make a trip to Menards tomorrow morning to get a longer bolt, washer, and nut of the same thread.