Almost any crank WILL bend if hit hard enough, especially those with only one front bearing and a prop hub 2 or 3 inches away from the bearing(G38, Sachs 3.2, US and Quadra 35-42,) and some others..The long cranks on some of the other engines that don't have a bolt on hub are usually soft and bend easily......If you bore a 1 inch steel block to exactly fit the crank you can indicate the end of the taper and see the runout..A lathe chuck good enough to do this wouldn't be for very long.. Hubs can also bend, the 6 bolt Sachs conversions by A&M and copies thereof are a good example...Most cranks will twist along with the bend...Hubs also bend..I have a 3W 150 hub here that was hit so hard that the rear of the taper, next to the case, is deformed about 1/8 inch....The thread broke off the end of the crank on that one...
FWIW..The cranks most resistant to bending are the cantilever cranks with the taper only about 3/4 long, from the front of the case..The front bearing is only about 1/8 inch away from the case and such a short shaft is really hard to bend...There's no way one of those can twist...
Putting an indicator on the end of a prop to check runout is mostly useless--Nobody's prop is that good.......
Best way to get the hub perfect is to bolt the engine upright on a mill table and use a nice sharp carbide cutter to face the hub while turning it slowly by hand...This gets it exactly 90 degrees to the crank......