While David Dickson was not a member of the Westminster Assembly, he did help to write the Sum of Saving Knowledge, which is found the complete editions of the Westminster Standards.  Dickson's Therapeutica Sacra is a fairly representative treatment of the issue of the nature of the Mosaic Covenant, as well as the relationship between the old and new covenant.  The chapter dealing with this subject can be read here.  Thanks to the folks at www.truecovenanter.com for putting this work in digital type.  The whole thing is a gem.