Right warren. I think you are touching on new ground here. Basically iva inspectors are glorified moters and dont have the first idea about this stuff.

Basically and i know its a shitter but have a word with tue dvla. I guess you are wanting roadworthyness thrown in.

I think as you are going alone and i have never read about anyone going as far as you with regards to safety and even seat mounting, you are in un charted terroitry.

And then cad designing on top. I think pf may be outta the reach of what you want and speaking on aviation forums better.

But good luck. Whatever it is sounfs awesome