You might want to pull it off and measure it,your damper length should be 3.400" if it is 3.875 you have a damper that is supposed to be a 351W or 302 H.O. with the Ford Racing .917 crank sprocket.That damper can be used on a 351C with the above sprocket but requires having .070" machined off.This was noted on the instruction sheet that came with my balancer.If you still have the old stock balancer,compare the length.