if you're going to put a kit on, you should be disassembling everything anyways to make sure your shaft seals and bearings, etc, are all in perfect condition. The other advantage to porting with it disassembled is you can get at it a lot better to smooth it out, etc. If you are gonna spend a couple hundred bucks, you might as well take the 2 hours or so it takes to dis-and-reassemble the engine.