M&J Wilkow, as part of a joint venture with DRA Advisors, completed its acquisition Wednesday of 11 Stanwix St., a prominent 23-story office building that once housed Westinghouse Corp. Marty Sweeney, M&J Wilkow vice president, declined to disclose a sales price. The seller, Munich-based GLL Real Estate Partners, paid $66.6 million for the building in 2011.