If you want easiest big bore go with the 540.you can get the piston from la sleeve.
They have a copper head gasket that?s 60 thousands thick, it will smooth out the power.
The head needs to be cut 3mm bigger, and grind the power valve to fit.
Just send the cylinder to get replated to that piston. You don?t want to use the steel sleeve.
As for the carb use a number 8 slide, it will give you a lot better off idle response.
This set up is a lot smoother and way more bottom end than kx 500, been running one like this for 12 years.
If you need to know more about this setup just let me know.
Just a word of caution, the advertised 540 is really only a 527 not 540, the bore is 88.4 mm. I'm not sure why they call it a 540, unless they have a stroker kit for the crank that makes it a 540.
With all the discussion about HP lately and whether we need more, I've thought about the big bores, and while I do think they have there place, I don't think trail riding is that place. Big bores tend to vibrate more than standard bores, they make loads of troque but lose some of the quickness. For every day riding I would go with modding the stock 86 mm bore. I only use mine for Hillclimbing, they get ridden 8-30 seconds twice and then back in the trailer, for that there fine but I wouldn't want to go trailriding one, my right hand goes to sleep as it is, I can't imagine riding one of those vibrating things for hours.