James,
Now don't hold me to this (I am only 5' 10"), but I think you will be pleasantly surprised with the flexibility of the seating for most attractions. Walt Disney World has been dealing with guests of a variety of sizes and ride needs for some time now, and many of the seating options are going to be just fine for you.
For example, I was recently on the new
Toy Story Mania attraction. I think you would find their standard seating to be just fine.
Perhaps a better way for you to get some comfort with the situation would be to review some amateur photos of ride cars and attraction seating at the
www.AllEars.Net website under "Theme Parks" and then "Special Needs Travelers". They have a great article titled "Walt Disney World at Large" that gives you some travel strategies, as well as the photos of the ride cars.
Finally, don't be embarrassed to ask a cast member when entering an attraction line if they think there might be an issue. They will know the attraction, and can spare you the time in line and any possible disappointment!
I hope that this helps!
Have a magical vacation!