Well, first of all, I'd say that while an identity column does uniquely identify a row, you still should have the business key as a unique constraint on the table. Auto-incrementing values shouldn't be the business key (which it sounds like you might be doing). That way, you never have to worry about suddenly having to duplicate the values of an identity column (which you shouldn't ever do).

The question for me is, what's the right clustered index on the table? Will most of the data access be through this single field, or through the compound of three integer columns? If the former, keep that as the cluster, but add a unique constraint to satisfy the appropriate structures. If the latter, drop the identity column and go with the three columns as your key.

Where possible, I try to avoid GUIDs, although I don't have the phobia about them that most do.