Mark:

My own take (and that of most NT scholars) is that Luke-Acts belongs to the same author. His writing is most naturally dated between the 60 and 80's (I prefer the earlier placement, but it could be later). The material is too linked together and the style is too similar to think otherwise. Whenever we post "proto" documents forwhich there is no evidence to support a theory, then there really is no way to argue against such a view, since the backdrop is assumed as present.

I have written full commentaries on Luke and Acts with introductions to discuss the details, if you wish to follow up. That Luke, a follower of Paul, wrote this is most likely. A key reason is that if authorship is a matter of selecting someone to look authoritative, which is often the claim of those who argue for another writer and later date, Luke is not such an obvious choice as a Pauline companion (Titus, Timothy, Barnabas, Silas would be more natural choices, being more prominently connected to him). Yet the tradition we have unanimously names Luke. Where did that unanimity come from if better "choices" existed? I find it likely the tradtion knew the origins and that this explains this result.

dlb