Many modern cams need dual springs even with lower lofts because of the fast rate of lift. If you are having the ehads doen anyway, I'd have the spring seats and guides trimmed for the positive seals now. Even if you dont need them right now, you may, and it's cheap to do now and you'll have better valve seals regardless of the spring. You can run single springs with std guides and std seats, but you can never run dual springs with factory seals or spring seats.