By Andrea Shalal WASHINGTON (Reuters) -A price cap on Russian seaborne oil deliveries being developed by the United States and G7 countries could significantly reduce Russia’s revenues while encouraging Moscow to continue to produce oil, 16 economists from top U.S. and British universities told U.S. Treasury Secretary Janet Yellen. The cap, agreed in principle last month by the Group of Seven rich countries, should lower Russia’s revenues by strengthening the negotiating position of any buyers, economists including Simon Johnson at the Sloan School of Management at the Massachusetts Institute …