Standard RH thread. You'll find a 13/16" long spark plug socket is the easiest to use on that one.
If you don't have a rattle gun, the simple way to lock the crank while you undo the nut, is to pull the spark plug, and feed some soft cord into the barrel, with the piston down a bit from TDC, but not all the way - you want all the cylinder ports to be closed. Then turn the flywheel CCW until the piston crown compresses the rope against the head.
