What version were you upgrading from? The big NCM change in 7.3 is that NCM no longer has a separate database - NCM's data goes into the Orion database now.
If you are deleting the Orion.Nodes entry, you shouldn't need to also call RemoveNode - that should be taken care of automatically.
Other than that, things should pretty much work the way they did in previous versions. AddNodeToNCM is still needed when adding a node.