I have found the best comps for houses like that are immediately surrounding it (not sure what goes into a builder's mind). Even if you have to go back 15 years, you can still try to match a sale from that time period. Of course use percentage difference, not absolute dollar difference.
You can sometimes look at exterior pics to--usually on houses like this the side windows seem really close to the roof--well, because they are. Also look for kitchen cabinet difference between top and bottom, and see how close the tops are to the ceiling.
At 6'6", any doorway header would be below 6'...
I think ANSI considerations are the least of your concerns.