I had basically the same situation in my 70's-built house, the closet doors went all the way to the roof, and were horrible looking bi-folds.
Basically what I did is framed in a header to bring the opening to 81" (remember to account for 1/2" drywall while framing):
Then some drywall and paint (note I didn't yet repaint the ceiling in this picture):
I had 4 closets like this. I'm planning on installing sliding doors, but sadly haven't actually done that yet (and reading the post on my blog, it's been over 2 years now... ugh). I actually just found out the other day that the doors with frosted glass in them we were going to use have been discontinued, serves me right for waiting so long.
The width is going to be challenging for stock stuff. If it was a bit wider, you could probably split the door into two by putting a small column in the middle, but that would leave you with a couple 3.5' doors, which are pretty small. If you went to bi-folds, you might be able to do a 4' and a 2' door, though that might look a bit strange.
A quick search turns up some custom closet door manufacturers, which might be an option to get multi-panel sliding doors, like this:
If you do this you can probably also get them 8' high, but honestly, even without the doors on, just making the opening 81" really updated the look of the house.
Yet another option is that you could shrink the width down to 72" (basically just extend the wall/framing on one side by 9"), and along with making the height 81", you're into a standard size where you can get both sliding or bi-fold doors off the shelf from any box store.
Good luck, and let us know how it turns out