One thing to always be sure of is where the bar is going to go if it either breaks loose suddenly or snaps back. Don't be there, especially if you have more than one person on the bar. I use an HF 27" bar, it's not required on a motorcycle (not much can't be accessed by an impact) but I often need a reaction bar for through-frame bolts that are placed so I can't grab a wrench on the other side. I'd use my nicer bars but they're not as long to hit the ground/table at a good shallow angle and the bolts don't have an unmanageable torque value for a regular 1/2"-drive hand ratchet to hit, it's just that they spin without loosening. Sometimes I grab a bungee cord to hold the socket/breaker to the frame tube if the nut doesn't give the socket good purchase.
If I had to do a crank nut, ideally I'd buy a spendy 3/4"-drive bar with an impact socket to match, and some very good pipe to snugly fit over it. I have seen something either from Lisle or K-D tools that uses an air hammer like a right-angle impact wrench, if the price was comparable, that could save effort. I think I skipped it over because the torque arm was shorter than I thought it needed to be and the hammer shaft was very long to reach oddball engines. If you had access to a welder, you might take a hammer bit and a serpentine belt tool and make your own.