Because of the equipment sub, a new crew of pilots had to be found. The 763 and 764 are operated as separate categories for pilot purposes. They actually managed to pull a Capt and F/O off of their layovers in different European cities and deadhead them into LHR on foreign carriers. Unfortuanately they could only come up with two pilots. Since the LHR-JFK leg is scheduled for over 8 hours and per FAA regs would require a third relief pilot, they had to schedule it as an LHR-BOS leg under 8 hours to make it legal while simultaneously positioning another 763 crew to BOS to complete the trip. While it is obviously not the ideal situation, I can tell you that Delta and Crew Sked went to unusual lengths to get this flight completed