I always thought that the NR750 road bike was as much an engineering exercise as anything else, just to prove they could. I guess most of the limited number they made never saw a road. I've never seen one.

To answer DCLUICE first question the reason they never really went anywhere with it was cost. For the relatively small performance gains it gives you over a conventional round piston the extra production coats are huge.

There are also a lot of technical difficulties with oval pistons, it's easy to make a round piston ring that expands and seals evenly but it is very hard to do it with an oval piston ring. Same with pistons, round things expand much more evenly than oval things.