I would say 88-90hp absolute max on a crank dyno. K&T does build wicked stuff, but I just donts see enough displacement to make those kind of numbers consistently. I do know we recently crank dyno tested a 6mm, 460cc, resleeved, and torque ported cheetah motor with pro circuit pipes and saw 92 hp. It made 87hp with ptr mids. This is all speculation, but I bet that K&T bike is really fast.
Look at it this way, the superior sleeve 10mm+ stroked motors back in the mid 90's made 110hp on the dyno. You get to a certain point with a stock cylinder (470cc-510cc I think) and you just cant move enough air and fuel through them to make a ton of hp. Thats why we saw the introduction of the 4-6 different aftermarket cylinder setups that are now available.