I sold a SB 727 set up out of a 318 car to a Air Force guy going overseas back in 1971 or 1972, he had a 1971 340 Duster 4 speed car that his wife couldn't or wouldn't drive due to the clutch or shifting, anyways he put the flex plate on wrong, it broke that flexplate and I now think it vibrated also. OP, look at the flexplate, the outer converter mounting ears should be further forward to the front of the motor than the center of the flexplate is What that does is allow the converter to spin without the converter hub being centered into the crankshaft hub By rubbing it is telling you that it is not correct, time to figure out what is wrong with it