I send my stuff to ThomasRacingService. I'm pretty much stock, but they will build to suit. Its the old saying speed costs money, how fast do you want to go? They are more than capable of turning out the rebuilds by Christmas and work on a range from Pro bikes,drag bikes/ drag quads amatuer racing and leisure bikes, single cylinder to multi-cylinder, even dual engines.
the Kawasaki-xpert is Dan Watson, father/mechanic for "Super" Dave Watson a very well known, pro rider. He is very smart when it comes to getting fixed on time or going fast on the kx's. Thomas is an expert on multi cylinder nitro bikes.
I am currently leaning to checking out Stewart and his R&D. I seriously think, for what I know, if its about getting the most out of your engine without going too far or guessing at mod combos, Stewart is the guy to spend fast money with. Not sure of cost, but what is the highest priority, price, turnaround, or results?