JM2¢?
Any quality damper is going to have periods of harmonic suppression wide enough to do something useful, even if it's not where you want.
The OEM damper isn't as accurate if the RPM range goes up significantly (you may reach another "order" that the OEM wasn't designed to handle), or the crank has been modified (lightened, light flywheel, stroked), and not blow-proof at high RPM (cast-iron) but will do a good job if new or excellent.
Remember: SFI cert. is only a safety check (it won't explode) and doesn't test for actual damping - let alone damping on a specific engine.
The closer the similarity between your engine and the model from which the damper was designed, the better the match. I'd rather have a Ford 300 damper on a 292 than none.
If you can't find one really close, the next best thing is to try to anticipate where the crank will suffer, and avoid using it either very hard or continuously at those points. For a street car, the engine may feel "buzzy" as certain speeds, and better slightly above and below regardless of what gear it's in, and regardless of power. Those are probably suspect points - drive through them, or around them. Don't do 200 miles at that speed.
With a drag car, they's pretty easy to avoid them since you pass through them. An LSR or boat is much worse, circle track very bad.
