In addition to the bolts, there will be a coolant
line and the gearshift tie rod still connected. Usually, the coolant
line is a slip fit and will come apart on its own. The gearshift tie rod is likely bolted together. There may be a rubber plug
part way down the lower unit. Remove this and you will find the clamping screws you need to loosen. The drive shaft will detach as you pull the units apart.
Also, you might get a gasket
set, as the lower unit provides some of the coolant channels to the power unit, and they do need to be properly sealed on reassembly.