did you pull the spark plugs? makes the engine easier to turn. I just tore down my 400, and found turning over the engine with a socket on the "Timing nut" on the right side was the way to go, I also had to remove the cam gear nuts to get the shaft out. are you sure the cam chain adjuster is not froze in position?, it should give you a little slop when loostened- but you still have to pull the gear to remove the cam.
good luck.