I think changing shaft diameter is not neccesary with the 2GM of earlier models. The later boats have a bit more powerful 2GM, hence the larger shaft. I have an older 2GM and had vibration. To remedy I replaced the cutless bearing, put in dripless PYI seal, new 3/4 shaft, had the prop reconditiond, replaced the motor mounts and removed the sound proofing and replaced it with acoustical paint called Silent Running. The motor purrs like a kitten. Still a bit noisy at idle but there is no vibration at all when underway.

David
#397