1)That's only about 800 km. for Lisbon. Widening the Atlantic that much really should not affect the circulation patterns. Closing the gap at the northern Pacific also should not make much difference, since there is almost no oceanic circulation through the Bering Straits. Otherwise, there doesn't seem any good reason to assume the global conveyor would be affected.
2) I think that the above is based on what you meant, but you should be aware that the prime meridian was not picked on any geographic basis. It was essentially a political decision, and the dominant factor was the preeminence of British trade, which always used the British navigation tables and maps with Greenwich defined as the prime meridian. International acceptance occurred in 1884. The French were miffed (they argued forcefully for Paris), and went their own way for nearly 30 years.