There is an RG500 engine been put into an NSR - looks very very well done.

I think you are giving the RD500 motor a bit of a rough ride - it's a good engine, not too heavy as a lot of if was magnesium. It's downsides are a poor inlet system.

90 deg intake boots, small carbs, small reeds and small transfers. But you can still get 110 rear wheel HP from one.