I just finished my 70 Dart with a 340 and 42RH conversion. I took it out for a test drive, however the vibration is so bad, I had to take it home. I can feel it idling in drive or reverse and continues right off idle. I brought it up to 35 mph and the vibration/noise increased with speed. I took it home, but am un certain where to look. The driveshaft, is new with joints (wasn't a shortened core, but built) the converter is new and supposedly the trans has been rebuilt (only real unknown) The 8 3/4 is also brand new. My first thought was the converter is externally balanced, but I didn't see any weights and I used the 340 flexplate. I am afraid to drive it as I don't want to mess something up.