Hi there, I have a 69 chevelle small block 350, 4 spd sag trans, total rebuild on motor, when I built the motor it sat completed for 2 years before I installed it, I bought a standard harmonic damper from advanced auto, and now with the car at idle I can see the damper does not run true, and I have alot of vibration at idle, when I take it on the freeway my hurst shifter really shakes and vibrates, could the damper create that much vibration? I have not checked the drive shaft for balance yet because it vibrates at idle. What size damper should be on a small block 6" 7" 8"