[Mach 1]

I did mine similar to nathan, but i actually removed the screws in the back of the cover. It was tight, and my hands were scratched, and a little prying helped, but it can be done. Discharging the A/C isnt required, but if money isnt a concern, just dump it yourself, then pay to have it serviced after you put it together. It sure does make things easier. If you dont want to dump the A/C, loosen the clamps on the engine side of the firewall around the a/c lines, and remove that long bolt that goes in the bottom of the heater box from the inside.

This will give you some room to move the box around slightly without opening up A/C lines.