LONDON—Finance ministers from the Group of Seven (G-7) said they made some progress on Wednesday at reaching a joint position on a global corporate tax deal, days before it needs to win over a wider international audience. “A common understanding was reached on some of the important open issues to support reaching final political agreement within the OECD Inclusive Framework in October,” the U.S. Treasury Department said in a statement. Britain—which chairs the G7 this year—brokered an outline agreement in June on a global minimum corporate tax rate of 15 percent and measures to squeeze more money out of tech giants such as Amazon, Google, and Facebook. Next week the Organisation for Economic Co-operation and Development (OECD), which has been trying to shepherd through tax reform for years, wants to get full agreement on detailed proposals from 139 negotiating countries. “Today’s meeting of finance ministers evidences the continued ambition and …