when is the norm directive?

Perhaps you can help me with a question I have regarding church government. Over the past few months I have been think about elders and looking at what the Bible has to say about it. This is what I have concluded:

A plurality of male elders is the the norm for NT churches.

The question I have though is when does the norm become directive. Mark Dever in his 9 marks of a Biblical Church says: The only two biblical church offices are deacon and elder. And I agree that the norm for the NT churches was to have elders and deacons. But how do we know that this is then directive for churches today. There appears to be lots of other examples of things in the NT church that are normative that we reject as directive. eg. they met on Saturday...

There also seems to be a whole category of people in the NT who can be classified as Paul's fellow workers but who were not elders or deacons but may have done elder like things eg. Apollos in Corinth, Timothy (was he an elder?), Epaphroditus.

Is the NT norm of eldership directive for us today or is a means to an end. That is, would Paul be happy with some other structure or office that achieved the goals of shepherding, overseeing, keeping the wolves at bay and teaching the word of God?

Thoughts? How do the Anglicans argue for their church government?