Since there are 31 degrees between the seat and 0.050" lift points, I would go with the LS6 springs. They are more than adequate at 0.551" max lift.

If the lobes were more aggressive (like 25 degrees between seat and 0.050" lift points), or you were going with forced induction, I would then use the Comp 918 springs. The increased spring pressure will help control the valves better at higher RPM levels.

If max lift exceeds 0.580" with agressive lobes, I would then use a good double spring, like the Patriot Golds.