Hi Brian,
Just took my A/C system out for cleaning and service. I would disconnect the hoses in the engine compartment nearest the firewall. On the inside here is a bracket up against the lower firewall on the passengers side. Near where your toes would be.
There are a series of 4 or so plastic plugs on the lower part of the A/C unit underneath the front deflectors. Pop the plugs out and you will see 7/16 in or so bolt heads and large washers. These bolts go up through the lower edge of the dashboard frame and hold most of the weight of the A/C assembly. I think it just slides forward and out after taking them out. Makes getting to the antenna a breeze. The passenger side carpet in my car was trimmed around the A/C. Don't know if it's original or a lazy prior owner who forgot to tuck it under the A/C before reinstalling the assembly. It's a simple job. Taking the compressor out is more difficult. Are you going to do this also?
Jeff C.
1970 280SL 4-speed