Hey man trust me.
I've owned several 2 stroke ATV's. Been working on them for 14 years.
Porting, in the hands of the right person, will be the best power increase for the money.
You can go triple exhaust port setup on a stock bore machine and have 2-3 times more increase than a bolt on 240 kit.
I waxed a guy with a 240 when I had my stock cylinder Blasty. And I also had the stock carb.
Try this, go to bansheehq.com and post this topic over there. (Those guys are generally more experienced with 2 strokes).
This is what I suggest. Find a good builder (I can personally ecommend RB Racing from 1st hand experience)(and no, I am in no way affiliated with him).
Send him your jug and head, and get it bored .010" over, get a weisco piston, mill your head just enough to where you can run super unleaded, and get the aggressive dune port. You will spend about $275 total, but you will be extremely happy. It will be money well spent.
Or you could spend more money on a 240 kit and be disappointed when you race a ported 200...