Put the monster on VP. Ask Hill Climb 147. He loves the stuff. It is great for race bikes, and requires very little set-up. Jetting is the change. There are a bunch of upgrades to make you scream.
Are you talking about a dirt hillclimb or the road race? NAHA just raced here, in Indiana, and they had a 0-540 class. It was mostly 450's, and had a qualifier round. Only top ten went on to race.
Either way, jetting, gearing, and tires are where its at. A kx 500 can be the fastest bike over most other cc's because of power to weight ratios and of course brutal kx power. The trick is getting the set-up correct.
I thought the 540 kit was a stroker kit for the Cr 500. It has a short stroke so, I think, they put a kx crank(longer stroke) in it with plenty of mods to make it happen. I first heard about the 540 kit on here. It requires that you lose the powervalve. If you do that you might as well get a CR.