Just saw this thread, hopefully I can help a little.
The brace installed in the car is actually Hank's seat bracing kit, graciously installed by Hank himself. We decided to install it after seeing pictures of a heavy 944 spec accident where the floor did in fact buckle and the seat moved. Luckily, in that case, the seat moved away from the roll cage and other objects, but it was enough to convince me that the thin, factory, floor sheet metal was insufficient for race seat mounting.
The metal in the bracing kit is much thicker than the floorboard and Hank made sure to attach it in the best way he could.
Here is a picture of the bracing pre-paint and pre-drilled. (sorry for the huge pic's)
Same kit installed in a late car with the e-brake still installed. Late cars are slightly different.
Early car again, w/ holes drilled, while being painted
My legs are long enough that I was able to angle the seat and move it far enough back that head clearance was not a concern, unfortunately, that doesn't seem to be your situation. Would a steering wheel extension possibly allow you to angle the seat back? I noticed that reclining the seat back just "1 step" also had the benefit of increasing head clearance, by lowering the seat, without gaining much leg distance, only problem was the steering wheel was further away.
Hope this helps,
Chris