Either the rockers or the valve springs need to go. The lift on the exhaust valve would be .644 using the 1.85s; that's way too much for the 918s. Plus, unless you have ported heads, there is little need to go much past .600. I'd swap out the rockers, and keep the lift at a reasonable level. You could also swap to a dual spring, but with that type of cam, it'd just make for needless valvetrain wear. I doubt that the valves would hit the pistons, as overall lift has zero to do with that, but those rockers move the valve off the seat quicker which could theoretically cause a problem. I'd say it's unlikely with that cam, though.