A new article has been published in Kant Studies Online. It is by Adrian M.S. Piper (APRA Foundation) and is entitled: "Reconsidering Kant's Self-Legislation Procedure". It includes, amongst other things, one of the most extensive discussions of formulas of the categorical imperative that you are likely to find. The article can be freely accessed and downloaded here. All articles published in the journal are freely available for download and consultation.