I can't see it. This using an impact business.
What is there so complicated about loosening or tightening a nut that requires such an over abundance in applied force?
If there be the legitimate reason, i.e. physical infirmary, is one thing and o.k.; but picking up a torque gun to save a little effort on behalf of your arms (or suffering your brain into a bit of creative thinking prior to pickling the poor thing against the night's cold), is patently inadmissible to my mind.
Find a pipe and a person and a piece of delrin (you can also pinch some of wifey's nylon cutting board...blame it on the cat...). It is suggested to find a pipe suitable enough to compel the cooperation of both the person and the motorcycle.
Impact wrenches were adopted long ago as a method of improving rate-of-production as well as consistency in accuracy. From there they trickled into the hands of the Great Unwashed (fitters and mechanics), then further to the feeble-handed or those sadly lacking in pipes, wives, cutting-boards and cats.
Anyway,
Subjecting the motor shaft to a bam!bam!bam!bam!bam!bam! hammering at 400 licks a minute at anything above 300 ft. lbs. torque seems to me contrary to mechanical usage ....
... figger,
even if you've used a jam bar, that set-up is not, in itself, perfectly rigid, therefore there is play in the torque path of those hammering shocks; That play rebounds under the backloaded force of the jam bar to be ready for the next smash. Result, Q.E.D., your wrist-pins are hammering on your wrist-pin bushings... for one thing..... And remember that you are pushing hard (again backloading) against the combined weight/resistance of the bike.
Not for me boys, just the thought of subjecting the internal works of a V twin mill to that kind'a heavy and repeating shock load, most especially when considering that the motor isn't turning over to spread out that applied load..... gives me the heebee-jeebees..... bad.