Please don't use an impact wrench on your engine anywhere.
You have to have the proper tools to tighten the nut, so you might as well make the investment up front. Then use them, along with two breaker bars, to carefully loosen the nut. One goes on the crowfoot, the other goes on the cam.
If you use an impact wrench you're asking for the chain and sprocket to resist the torque, because there is no way to hold the cam with a socket over the nut. That's asking for trouble with the chains and the sprockets, to say nothing about the possibility of snapping the nose off the camshaft.
Also, a 46mm socket isn't exactly cheap. If I had it to do over I would buy Stomski's tool, it looks like a slick solution.
911 Cam Nut Tool
