[Tim Corcoran]

I have a 67 GTO that I recently purchased. Its a great car and it very fast with a butler built stroked 455 with ported eheads hyd roller and Doug's headers. It has an M20 transmission with a Centerforce dual friction clutch. There is a pretty significant vibration at 1,800 RPM. It's not the driveshaft and it's not the transmission because it has the same vibration in neutral without the car moving. I believe it's either the engine or the clutch causing this vibration. I was wondering if anyone has experienced this issue? I only notice it at right around 1,800 RPM. Any ideas? Could this be caused by a malfunctioning hydraulic valve lifter? Could the pressure plate/clutch be out of balance?