I'm not tall - I'm about 5'9" (when I don't slouch).
My left elbow rests on the door bar comfortably. I have added a pad at the front edge of the door bar for a knee rest.
I originally bolted my seat directly to the floor. I later added movable seat tracks (as shown in the "finished" picture). I was getting too much flex with the seat tracks, and have since removed them, bolting the seat directly to the floor again.
I bought some convoluted plastic tubing (similar to shop vac hose, but a little stiffer) at the hardware store that I used to mock up the position and shape for the side door braces. Stu Galbraith of Weldcraft then fabricated my design in steel, and welded it into the car.
Jeff