Got the hinges in.
I prototyped the hidden hinge arm, so the geometry works.
I am thinking about getting some arms waterjet from 3" steel billet, but I can probably make some from a couple layers of 3" 1/8 plate stacked after some precision bending.
This would have been easier with junkyard hinges but I wanted to retain the bluebird air ram and pivot for opening and closing.
I also got the stair floor pan in but forgot to take a pic.