You should make a tool to restrain the cam gear, similar to the SVO tool. I made mine out of heavy section angle iron, and welded two 5/8 inch diameter pins on it to engage two of the three holes in the gear. The angle iron is just over two feet long. With that installed, the nut can be removed/tightened. It's possible to leave the crank and cam gear meshed, and then block a crank counterweight to allow the nut to be undone or tightened, but that's only an option with steel timing gears. With the fibre ones it's not a good idea to impart the torque needed through the two or three teeth that are engaged in the crank gear.
Removal with an impact gun is ok, but to install that way....you better be good or the cam snout can be broken off.