ive currently been having trouble with my 283 and its harmonic balancer even though these motors are balanced internally i have found that the 283 ( cast iron crank ) and 327 ( forged crank ) to be using the same type of balancer now the real problem lies in the fact that the 283 had a press on balancer and if you start to change parts like a healthier cam that the internal balance then becomes slightly different so the simplest cure is to drill and tap the end of the crank. good luck to all the guys who haven't given up on 283's