Okay, when I used my Sparco Sprint seats in the Suzuki Swift GTi, I used the 3" belts w/ snap-in mountings. I had to fabricate my own mounts out of 1/4" steel- welded- and use ASE fasteners to bolt the seats to the bases. So if you stick with FIA certified seats and hardware (I doubt you'll need to fabricate mounts) you should be fine.

About airbags: Federal law prohibits the removal of airbags. But the law is rarely enforced-usually. Keep this in mind. I had passive seatbelts in the Suzuki, I ditched them in favor of the Sparco harnesses, and never had any trouble with the law.

Regarding the safety of racing harnesses: Spend money on quality, FIA-certified 3" belts. Keep them comfortably snug when in the car. The belts should not have any slack in them while you are driving, because if you get in a bad wreck, you want the belts to restrain your body as the car decelerates. If the belts are slack, you will be injured as the loose belts "catch" your torso-resulting in bad bruises, possibly broken bones.

So all in all, buy quality and use the harnesses correctly and you will be at least as safe as stock, if not more so.

Hope I helped.

Dave