There are two "LA sleeve 240 kits".
One is a complete replacement cylinder that bolts onto your crankcase with a new piston to match.
The other is a sleeve kit which is bored into your stock cylinder with a new piston to match.
The replacement cylinder has a MUCH better port layout than the stock cylinder (which is that "room to grow" brandoz was speaking of) and it's relatively bolt and go.
The replacement sleeve type uses the stock port layout which still has to be ported after the sleeve is installed. Installation of the sleeve is probably about $150 at a reputable shop and then porting is extra. By the time you have paid for all of the goodies with the stock sleeve, you could have installed the replacement cylinder and been done with it and still had your stock cylinder on the shelf.