You don't NEED the impeller removal tool, but it helps. You can grip the shaft with some vice grips and use it as the tool. Just heat up the impeller so the locktite will release.
But, the tool can be gotten from ebay for $15, and I recommend that so you don't bung up your shaft.
Oh, and my brother, who is a microsoft systems engineer, told me to keep lots of beer and COLA around. Start with a beer, then alternate a cola in. In my case, caffeine in the cola kept me up all night, and the beer kept me calm and from throwing the computer out the window.
Should work the same way for working on the boat.