there were a number of two stroke mopeds from europe in the 70's that had oval pistons, apparently helped make wider ports without having the rings bulge out into them so bad.
they were not made for long though, so its hard to say wether or not it was worth the extra manufacturing expense or not.
-Owen
the rings were 2 piece. and there was 2 flat sides on the pistons. 8 valves per cylinder. 2 spark bolts per cylinder.