Removing the big Black box under my dash for the A/C..

It has four studs sticking thru the firewall with nuts under the hood. You have to remove the heat box first, then the a/c box.
This is how my 72 came out, they changed in 73 but should be similar.
If your car is factory air you need that box for defrost and heat unless you find a non a/c heat box to install.