I just did a Homelite 25cc for a student. The only tricky thing we did was add a pin to the piston, use a Frank Bowman ring made for use with a pinned piston, and then ground out the bridge in the exhaust port. A gutted carb with two large outlets and a 11mm carb were added. Stock magneto ignition. It turned an APC 15 x 8 prop at 9000 after only one tank of fuel. That would be about 8200 or so with the more normal 16 x 8 prop. Not bad for so little effort... If you are nervous about modifying the piston like that, Frank Bowman will do it for you for a nominal fee.

Of course the 30cc doesn't even need that done as it doesn't have a bridged exhaust port.

AV8TOR