As to the second part of your question, the answer is "Probably not". An inline six is inherently balanced, so minor variations in the weight of flywheels and dampers rarely cause a noticeable vibration. Each component is balanced separately so unless your 302 has a heavy rod or other flawed internal part, a balanced flywheel, clutch or damper is not going to change that situation. Not to say that balancing a six isn't a good idea, but it isn't critical for normal usage.
Not so with a V8, which has a "rocking couple" effect with rods and counterweights flying around in different directions. So what you were told does apply to a V8, but in general, not to a line six.
