66 Mustang, 289 engine (C-code) with manual transmission, originaly an automatic. I am having a vibration issue with my engine...I think I know where the problem lies but some outside imput may help me. The vibration varies at different rpm (this is neutral, clutch engaged, not moving) I had a slight vibration before I did some work on the car this past winter, however it never caused any problems that I know of. (no main seals leak oil). I replaced the iron flywheel with an aluminum and also put in an aluminum drive shaft(not at issue here) and a Center Force Dual Clutch. I used the 28oz counter weight as was directed. It seems that the flywheel is the issued. Any one have any thoughts. Racer00