The roomettes are smaller than 6’6” which is my height. I fit in just fine. On a Viewliner (single level) I have to remove the seat backs off the wall. (Pull from the bottom and swing up, then off the hooks on the top. Clean the area behind the seat backs.) By removing the seat back you get to use the full space. Otherwise you lose several inches on each side, as you can’t fit the feet or head under the seat backs. Strange thing is that I don’t have this problem on a Superliner. Superliner are a bit bigger but also a different design.
As for your girth, if you toss an turner at night it going to be fun. Those are tight spaces on a Viewliner. Again a bit better on a Superliner.
Your size will not prevent you from travel and enjoying yourself. You just might be surprised on how much dirt collects behind those seat backs.
Happy trails from a taller traveler.