The old ones have seats with about 72in of lie flatness which is 6ft. But unless you sleep like a Victorian ghost, most people bend their knees or legs somehow. My friend that is 6ft4in has no issues and he’s tall and wide.
Most of the new ones are 76in to 82in. 6ft 10in is pretty generous. And if you need longer, there are first class seats which are full beds and you’d have no issue.
I fly in a pod every few weeks for 12hr+ flights and it’s very comfortable. I am hoping blimp travel makes a come back as I’d love to take the scenic way back with a full suite one day.