I have a 69 Camaro with a 94 LT1 engine and a Richmond 6 speed. At 3500 RPM and above there is a vibration, sitting still or driving. I picked up a used flywheel at a swap meet (small dia bolt pattern) had it resurfaced and installed a new clutch assembly. Is there a balance problem with the flywheel as in internal vs external incompatibility. I don't know what the flywheel came from and have not been able to find a listing for the casting number. Due to other circumstances I have changed engines ('88 350 to the LT1)and the vibration is still present. Any ideas?