[Early_S_Man]

Osidak,

The upper nut is a 10 mm barrel nut, requiring a 10 mm hex drive bit.

The easiest way to get at it is by putting the tail up on jack stands, and remove the left rear wheel. You can reach over the transaxle, and get to the barrel nut with a long extension to get the ratchet back past the body of the starter. Good luck!