Scott Charlesworth has an interesting article in the latest issue of NTS:
S. D. CHARLESWORTH, 'T. C. Skeat, P64+67 and P4, and the Problem of Fibre Orientation in Codicological Reconstruction' New Testament Studies, Volume 53, Issue 04, October 2007, pp 582-604
In this article Charlesworth argues that P64+67 (Matthew) and P4 (Luke) were quite separate multiple-quire codices written by the same scribe. He makes additional criticisms of Skeat's arguments in NTS 1997 (already subjected to a 'telling' critique by Head in NTS 2005) relating especially to fibre orientation (to which Skeat paid insufficient attention). An interesting study. Note - this was never a four-gospel codex.