I have a 3-wire connection for the clothes dryer, and I would like to make it compliant with current code the simplest way consistent with reasonable safety. I haven't looked at the connection block but it must be that the neutral is bonded to the chassis because the chassis is grounded.
The heavy ground wire that leads to the panel is grounded to the cold water pipe supplying the clothes washer and is exposed right next to the dryer. I could connect a wire from the ground terminal of the dryer to that ground wire and not change to a 4-wire plug and cord. In the connection block of the dryer I would remove the neutral to chassis ground bond.
Code violation? Someone could later disconnect that ground and the chassis would not be grounded. I could change to a 4-wire receptacle and connect a ground wire inside the wall or outside to the nearby heavy ground wire going to the panel.