Ok now there is no better way to visualize the magnitude of this truck without seeing it.
So I got the rails today. They are 35" long that's a 490" wheel base I believe.
Those are stock KH rails next to mine.
The box is the proper length but a little higher than the sleeper will be. However it is just under 13'6" as it sits...
There is still 13" of frame behind the sleeper. that's 182" 15"
-Mike