I too have seen machine shops store them short term standing on end. That's what I do too, short term. But for any longer time period I lay them on their side, and if there are not enough load bearing contact points, I use whatever I have laying around to create more. Just put something under the crank to dissipate the load more evenly across several points. Standing on end creates a risk of knocking the whole thing down by accident and ruining it that way.
REALLY long term storage would justify making a cradle out of wood to hold it at each main bearing journal. Or if you have the opportunity, leave it sitting in the engine block on some old bearings.
