A rev limiter needs to be in the ignition box or the ECU, not the distributor trigger. Most MSD, Crane, Mallory, and other aftermatket ignition boxes have adjustable rev limiters built in. All aftermarket ECUs have provisions for a rev limiter.
Running a L6 engine with stock valve springs above 7,000 rpm will reduce the rating of the springs. The springs get softer by some small amount. ITS racers, who have to run the stock valve springs, tend to replace the springs a couple times a season of they are regularly running the engine over 7,000 rpm on the track.
Also, a rev limiter does not save you from a bad downshift.