Here are some links to harness bars made by Brey-Krause. They are as good as it gets! The first one for a C6 Vette and it would be mounted closer to shoulder height. The second is for an M3 and mounts down to the lapbelt seat belt points. The final is for a Mini and is pretty self explanatory. In the end these are highly engineered devices to ensure safety! Be very careful in designing anything that your life may depend on. Seat belt angle, seat type and belt connection can really make a difference. If you are not familiar with basilar skull fracture read at the bottom. I know I'm being over dramatic.
Basilar skull fracture is a common cause of death in auto racing accidents:
* Formula 1 driver Roland Ratzenberger in the 1994 San Marino Formula One Grand Prix
* Indy 500 drivers Bill Vukovich and Tony Bettenhausen
* NASCAR drivers Dale Earnhardt, Adam Petty, Tony Roper, Kenny Irwin, Neil Bonnett, John Nemechek and Clifford Allison
* CART drivers Jovy Marcelo, Greg Moore and Gonzalo Rodriguez
* ARCA driver Blaise Alexander
Other drivers survived their Basilar skull fractures, including NASCAR's Ernie Irvan.
To prevent this injury, all major motor sports sanctioning bodies mandate the use of head and neck restraints, such as the HANS Device.