The issue here is safety. I would never put a 4 point harness in a car without the proper cage/ seat mounting setups.
Here is my reasoning.
A 4 point harness or any harness for that matter is designed to do one thing and one thing only, keep you in the seat. Without a cage this can be a serious problem in the event of a rollover. The seat and harness will keep you upright while the roof comes down.
Another problem I see all too often is the improper mounting of the harness belt. The top should be no more than 12 deg down from the shoulder line to the mount. The mount should be as close to the rear of the seat as possible, any slack can yield movement in the case of a rollover. Harness belts will stretch, more than you think. With the bar directly behind the seat, the belt should be about 1.5" below the shoulder line. If the belt is mounted higher then you run the risk of slipping out of the restraint during a rollover. When the belt is mounted to low then the vertebra in your lower back will see the brunt of the force from the rollover causing injury.
When it comes to the mounting of seats there are also several things to be concerned with. A harness is designed to be used with specific styles of seats. “Stock Replacement” seats are generally not designed to be used with a harness. You need a seat that has proper support in the shoulder region along with something to help restrain your hips. This will keep you body secure in the proper position for the harness to work effectively in the event of a serious rollover. The seat mounts should be more then secure, they need to be part of the chassis / cage. When you put a cage structure in a vehicle you need to secure the seat mounts to the cage structure. This will ensure that if the cage is to move so will the seats. Creating one complete structure in the cab region is important for this reason. I prefer to use 5 or 6 points for mounting seats in road cars. If you only use 4 points the seat has a tendency to flex in a rollover, regardless of the manufacture. If you do use a 4 point seat mount, then it’s especially important to add material to the mounts to create a sold structure. Another issue is the use of sliding seats with harness setups. The teeth or pins in the sliders can break due to excessive force. If the seats are not properly installed then they will cause a failure in the restraint system.
Although harness setups are cool, they can also be extremely dangerous when they are installed improperly. I don’t want to sound like the safety Nazi, but I see harness setups installed wrong all the time. I have included a few pictures to explain what I’m talking about.
Safety is always above style, IMO.
The GMR.