Kenneth A. Adams, A Manual of Style for Contract Drafting, has been published by the American Bar Association Press. At the book’s site, you can see the table of contents, and there are also articles by the author. The site also tells you how to get hold of the book – it was only published in July 2004, so it’s rather scarce as yet.
From the back-cover blurb:
bq. The focus of this manual is not what provisions to include in a given contract, but instead how to express those provisions in prose that is free of the problems that often afflict contracts. This manual highlights common sources of inefficiency, dispute, and misunderstanding and recommends how to avoid them. It offers a level of practical detail not found elsewhere in the literature on drafting.
I see the author originally studied medieval archaeology at York University.
(via Mark Adler of Clarity)