I'm not familiar with that inertia reel. If I were buying aftermarket belts, I would most certainly buy them with dual-sensing reels, that both lock up based on webbing payout speed and inertia/G loading. All new cars use this type of reel. Even with low elongation webbing, you would be amazed at how close you will get to the steering wheel in a real crash. Hopefully what you have it designed for the mounting location it is in. On a separate note, the early 240Z belts without reels are actually better than with reels. The only purpose for reels is freedom of movement and convenience. Inertia reels do not make you safer in a crash as compared to belts that are hard mounted to the vehicle structure, as the 70 and 71 Z belts are. This is akin to race cars which do not use inertia reels. But there is nothing wrong with adding them to your car as long as they are installed properly.