Thanks Gary... I'll post a little more here and then maybe some in the "Opel Parts Suppliers" forum or the racers forum.
Most of our stuff is intended for the serious racer. It will work for the street too, but since it is no compromise, "hard core" stuff, it is also expensive. The best example I can think of is the fuel cell mentioned at the top of this thread.
A gas tank is not much more than a "tin box" that you pour gasoline into. Then there are cheap "fuel cells". I use the quotes because they are not fuel cells at all. Rather, the cheapies are just plastic boxes that you pour gasoline into.
But if your life depends on it, then you want a REAL fuel cell. This is what is required by most racing organizations. A fuel cell is a deformable bladder. It is made of very tough aerospace "stuff" and is very resistant to tears or punctures. (I'm not sure the exact composition of the "stuff", but ours has FIA certification and is legal in every racing organization in the world.) The bladder is also filled with foam. The foam is also a fire retardant and helps to keep the fuel slosh to a minimum. Also, the 'cell comes with check valves in the openings (filler neck, vent tube, fuel outlet, ect.) so that if you end up upside down, the fuel won't come back out the fuel filler neck or other lines.
For our fuel cell, the bladder is custom built to fit into an aluminum container that will go into the original fuel tank location. (It even bolts into the original mounts.) The 'cell comes with the container and a remote fill kit. Our fuel cell is $1390, but you'll also need pump(s), a pressure regulator and steel braded fuel lines. So by the time you're done, it will cost $1600-$1800 for everything. As you can imagine, we only sell one of these for an Opel GT every two or three of years.