B&S Engine Smoking Like Crazy? Head Gasket Test and Fix - John Deere D110 Riding Mower

Troubleshooting and repairing a John Deere D110 Riding Mower where it is blowing a large amount of blue / white smoke out of the exhaust especially after engine warms up. Customer reports that mower runs but when it warms up it starts smoking when throttling up and down.