Ken, I would guess, if I understand your question right, that it would be easiest to position the ends of the curved cruck blades up when hewing. This is because that is how it would want to sit naturally. If the middle sags down, then its hundreds of pounds of weight will help to hold the whole thing in place to hew. If you'd place the middle so it arcs up, then you would be added the timbers own weight to its already annoying tendency to want to move while hewing. It seems to me it would be very hard to do it with the ends pointing down.