First of all I think that your screwing up by using springs that are only .03 taller than your cam lift. Your just asking for disaster if you float the valves or you get coil bind.

For just a few more dollars you should get springs more like max lift of .560 or so. They will run cooler and last longer. I always ran higher rated springs with my H-flat cams. Normally 135# closed. that way your worry free of valve float if your running a 7000 rpm red line.

With small H-flat cams like yours long slots are not needed