First of all, that's not the best way to lock up the engine. Unless you really hate that piston, rod & crank.
Better to put the clutch basket back on and use a penny or someother soft metal wedged in the gears. (between the primary & clutch)
If your impact isn't turning it, you may need a breaker bar.. Plus, so that you have enough leverage, put the engine back in the frame. I find it's easier to break the really tight fasteners on an engine while it's in the frame, then once all that stuff is removed, you can pull the engine out and everything else is cake.