How difficult is it to re emble a upper lower unit on a mer cruiser?

Ihave a mercruiser alpha one gen ll with the upper lower unit totally disembled.(bought it that way.)Marina told past owner it neede boots.I'm uming they are talking about either exhaust or axle bellow or both.Got a seloc mercr. sterndrive book,trying to figure out if all the parts are there or if marina needed some off it.Also how do you check bellows?check for rips?