my buddy has had bad luck with the federal mougal lifters, lasted like 2000 miles. put comp lifters in and no problems. i run comp lifters in all my motors. works just fine.
i believe the lifters void the warenty, but the springs are just a recomendation don't void the warrenty. if i miss read the instructions, then all my cams are void if the cam takes a ****. i use the Z28 spings.