I just pick up a 66 mustang. It has a 302 and the factory auto trans. When I picked it up I was told it had a bad harmonic balancer. I replaced it and the vibration got a lil better, but not gone. I doesn't shake on idle but if you rev it in park it vibrates bad. If you drive it it shakes in the mid rpm's but if you stand in the gas is clears up under load. Be for I got it the car was sitting for about 10 years. I checked the plugs and they all look like they are getting a good burn with a light brown color. I pulled the belt to make sure it wasn't the fan. any help would be awesome. O and I don't know what year 302 is in the car. Help with that would be cool to. It has a Holly carb, EB intake, Tri-Y headers and full Malloy ign.