Are you trying to out-stubbon me!? Good work son - much respect for trying, no matter how futile your efforts.
OK look, here's the deal:
VMX247 asked me the exact same question a few weeks back. Apparently some guy in WA bought a CR250RF in the mistaken belief that it would be eligible for pre-85 racing. I did some research on 84 vs 85 and concluded pretty much what Shane said: Not completely different bikes, but no cigar either.
Remember than in WA, the term "Pre-90" is even dirtier than it is here in NSW - the bike is useless to the bloke if it can't race pre-85.
The way I saw it, if the bike's owner could bring the engine back to a 1984 engine, it should be close enough for club-level pre-85 racing - the important performance bits would be the same/close enough.
When this thread sprung up, I assumed that it was prompted by the same bloke (I still don't know if I'm right or wrong, BTW). I'd had some time to think about the bloke's predicament and about what I believe is actually good for the sport of VMX.
Given the current health of the sport, I honestly believe that a bike with no performance advantage and that's fundamentally of the same era should be allowed to race among the kosher pre-85 bikes, which lead to my first contribution to this thread.
The alternative is to tell the guy with his nice RF to f$ck off and almost certainly risk losing him to the world of VMX.
You know the rest of the story.