Re: choosing a crank shaft
To pick the best one you'll need a couple V Blocks and a DTI (Dial Test Indicator). A lathe and a DTI would work too. A local machine shop might test both of them for trueness too for cheap if you don't have any of the test equipment mentioned. Now keep in mind with a single cylinder engine it's pretty tough to get perfect "balance" but if you can get your cranks running as true as possible you should end up with a fairly smooth running engine.