1969 383 Magnum. I am having a bad vibration at 2500 RPM it seems to be mid car no noise however just vibration. This car originally had an automatic transmission in it and now has a 4 speed and has had the vibration since it was purchased by my nephew. I have verified the harmonic balancer is the correct one. He was told the drive shaft could be to long and seemed so to me we had it shortened and balanced. I just pulled the transmission to check for the pilot bushing and it has the bushing but the yoke would not come out without a come along and hammer. Could be because he kept driving it with the vibration. Only had the four lower bolts in the bell housing. The first time we pulled the drive shaft it came out easy. The splines on the yoke and transmission look OK but will not slide together now. The clutch and pressure plate looks good also. I also put the car up on stands and ran it can't feel the vibration. Had the tires spun balanced also. Still was vibrating when on the road. planning to get the trans checked while out of the car. Could the bell housing flex with all of the upper bolts missing. The flywheel ring is a #2843 214 the original Flywheel should be #2843 211. The Flywheel that was installed is for an eternally balanced crank I believe. Hopefully I will find out next week.