My Woods RM306 was originally sold as a side discharge, but came convertable to a rear discharge just with the addition of a plate on the side. I think the thing that made it most convertable was that there was minimal baffling underneath. Because of this it functions real well as a rear-discharge but may have been a little weak at sending all the cuttings out the side.
My guess is clogging occurs on these other units because all the baffling is keeping too much of the cuttings stuck under the deck. By the way, my blades rotate counter-clockwise. I've never heard there was a standard one way or the other.