Temperature door will not move.......

[spudder]

I have checked the function of all the AC diverter doors on my '71. The temperature door in the evaporator housing is stuck and won't move with the lever. The cable is free and moves easily. I think I am going to have to remove the evaporator housing to access the flapper. What is the procedure to remove the evaporator/blower housing? How difficult a job is it?
The truck has been sitting for 30 plus years so it's probably a good thing to check all the components. It was a non AC truck that we converted, but the AC system was never charged.