I don't think it's that critical. I seem to recall mine is, as viewed from behind, clockwise on the right and counterclockwise on the left. But I'm guessing that the other way might be almost as good, and possibly less vulnerable if one prop ends up putting out more power than the other at some point. However, I haven't had trouble with that.
My twin pusher has detachable prop bearings, so it would be easy to do the other way. If I recall it's 24 or 26 inches and packs in a slightly extended computer keyboard box.
In this picture, it seems to be the other way around, but maybe I didn't pay attention, since I was just assembling it for the picture:
Twin Pusher set up