fairly easy if you take your time. after you do it a couple times its like second nature.
i ran a stock unwelded crank for a year because i ran out of time last spring and needed the bike together, i trued it and threw it in on a dune ported stock cylinder. when i pulled it back out this winter it was a few thousands off on the PTO side webbing from crank twist. if it gets bad enough it WILL tear shit up and a failed bearing will kill a top end.