Peter, how about rollers (round fence posts/ peeler cores) or skid logs for moving big logs with a redirects from your pulling power (truck?)? I've moved a roughly (green log weight estimated) 2000 pound log with a 2800 pound machine by using skid logs.
When logs are rounds, they can be wrapped with a winch cable to roll them. Roll them into a balance- point pivot (chunk of wood) to pivot/ rotate to adjust the rolling path/ turn a corner.