Hi Mate
I think you will have to look into what class u can race in.
I`m pretty sure here in aus you can not run in production as the nsr250 is not an aus production bike .
Looking at a few race sites you will be looking at pre-modern f3 class(90-95) new era (81-89)
Have a look here http://www.postclassicracing.com.au/pages/raceclasses.aspx