Removal... Its actually very simple.

Inside... First on the inside or the car unbolt the bolt that connects the mast cly rod to the brake pedal under the dash.
That's it for the inside or the car.

Under the Hood... First Remove the brake line & the larger fitting that connects it to the mast cly, you will most likely need to put it in the new one. Removing these parts now is easy because the mast is still bolted to the car.

Remove the 4 nuts careful not to drop the small l shaped bracket on the top left bolt, I think it keeps the wires neat.

That's it, slide the old easy cly out, and remove the old gasket. I then sanded & painted the area. On my car the mast cly had leaked fluid on the firewall & rusted it a bit. The following is a before I painted it with a matching color photo.

I reused the old gasket, but also applied silicone to the back of the mast cly where it joined the firewall to keep water out.

Installation...

The Spring... You have to swap the spring & clip from the old mst cly. The spring shown in photo is what helps return the brake pedal to the up position. If yours looks old replace it...but ahh...I don't know with what or where you can get one...

Here is that spring & clip that you have to use on the new mast

 

Inside... just the reverse, bolt the rod back to the brake pedal.
Good time to check if the brake light switch works or is in the right position/

Under the Hood... Just bolt it back up with the 4 nuts.
Install the fitting into the front of the new mast cly if it doesn't have one the fit & tighten the brake line in.

The new one also had a bottom port, since the original didn't you can keep the plug on this.