If a dampner is designed for a specific engine combo, the diameter doesn't matter. It's the distribution of mass relative to the diameter of the dampner that counts. There are small Chevy dampners at 6.29, 6.325, 6.6, 6.75, 6.875, 7.17, 8.0, and probably a half-dozen more. If they're designed correctly, and have the weight in the right amount and in the right place, they do the job.