this is close (5/8") to the stucco wall. (http://usera.imagecave.com/threadbare/DSCF1287.JPG) Will I be able to get the joint hot enough to solder, or will the stucco wall suck away the heat?

You already have a threaded adapter coming out of the wall with a threaded PVC coupling connected to it. All you need to do is unscrew the coupling. Why do you wish to unsolder a good set up? Good luck, Tom