QUOTE (Jeff94TA @ Oct 12 2011, 01:16 PM)

QUOTE (Blainefab @ Oct 12 2011, 03:13 PM)

So this combination cannot be mounted without violating at least one of the mfr usage requirements.
I'd like to say I wasn't aware of that but I did understand before I ordered the brace. Do you think I'm being unsafe? I respect your opinion very much and if I'm being foolish then I'll shelf the brace until I get a real seat for the car.
I think you WERE being unsafe - with the amount of movement of the seat, its ability to protect you in a wreck was compromised. You recognized that and took steps to fix it - I would not call you foolish for your selection, that is what has been made popularly available from an industry that doesn't really care about anything but selling parts.
Those parts have been sold for at least 10, maybe 15 years, virtually unchanged. The Corbeau seat was not designed to go in a race car, and the IOPort back brace was not designed to go on a fiberglass seat.
In the last few years, club racing recognized the need for sturdier seat mounting, and an easy solution has been to adopt the back brace. Some rules simply say 'back brace required'. Rulebooks can't tell us how to build a safe car, just set minimum standards, and in general, require that equipment be installed per the mfr's instructions.
A better solution is to mount the seat such that the mounting area does not flex. Bottom mounting any seat puts bending loads in the area around the mounting bolts - take the seat cushion off and watch the seat bottom flex as you reef the body of the seat around. You might see stress fractures radiating from the holes. Side mounting is much better - it puts shear loads on the mounting points, there is little or no local flexing of the sides of the seat. The rest of the seat will move a lot less.
The slider is another source of movement. All sliders have slop compared to a fixed mount. The one that seems to be the least sloppy is the Sparco double locking slider. If you don't need to seat wildly different sizes of drivers I strongly recommend solid mounting it, with side mounts. Other sized drivers can sometimes work by mounting the seat for the tallest, and adding padding for the shorter driver.
Seatback braces - rules are rules, braces are here to stay. The IOPort brace is specifically designed to be bolted to the seat back. If not bolted, the flat part of the brace can flop down horizontally and knife thru the seat. Bolting works fine with an aluminum seat, they are not supposed to flex, and a few holes won't harm them. Bolting onto a fiberglass seat will act much like the bottom mounts - put cyclic bending loads on the fiberglass.
There are a couple seatback braces made specifically for fiberglass seats - They attach to the rollbar only, and press against the seatback with a large padded area - designed to limit the extension rearward, gently, without causing any local points of stress.
this is one:
http://www.bkauto.com/porsche/r9020.php 
and I make this one: