Hey Ron (I assume), I'm a fellow Eugene person and am searchign for someone that can help me with my shower. I have a premade shower pan (jacuzzi brand I believe) - 34x48". It's set and plumbed in. My carpenter put up greenboard around the shower (he realizes it was wrong now but thats how he did his personal shower and never had problems with it). From what I gather the best thing for me to do right now is to install Kerdi over the green board. Is this something that you know how to do?
Go to www.schluter.com and review the installation documents for this system. It is very user friendly and the drywall you used will work behind it. Although normal drywall would have been better, since it is much stiffer.