Thank you all for your words of wisdom!
I am sure I will love the experience of WWOHP I just am a ride junkie, so I know it will be a huge disappointment to not get on. I'm happier being prepared for the blow than getting cold water thrown in my face there though, so thanks for your input.
For now, I am thinking I'll be a go, after reading reports here and hours of internet research, and finding the seat measurments and comparing it to a bunch of chairs in my house. But I guess I'll know for sure on Friday!
And if I don't fit I will be consoling myself by buying the $100 houserobe I promised myself I would not buy.
And of course, as pissed as I will be it will make pulling into Disney the next day all the better, because I'll be returning to my happy place where I fit every ride!