If you have the money a CT Racing 240 kit is the way to go a little over 1500 bucks but it comes with everything new jug, new carb, new pipe. if not the vitos 12-port is ok, about 500 bucks. But it deffinantly needs porting the stock porting sucks. if you want to go a little cheaper then just send your jug to Flotek he can get more power out of your stock jug by just porting it than you will get out of the stock vitos 240 kit. I got the vitos kit and had Flotek port it and am very happy with it. but keep in mind that any of these options is probably going to mean a new carb, pipe, and reeds.
As far as boring goes the only way to tell is to measure the cylinder and call the piston maker to find out the excact size of the piston. I believe most cylinders require .0015" to .003" of piston to cylinderwall clearance and at .005" it usually time to bore but remember after a hone and break-in cycle the cylinder will gain about .001" so if its .004" before you hone it, it will be .005" after its broke-in and thus loose enough that it may cause the skirt to catch a port.