If stock rockers scuff the valve stem tip, they do it because the geometry is wrong. You should be able to put a very thin piece of paper between the rocker and valve, turn the motor over and not tear the paper. It will compress the paper, but should not tear it. I learned this by talking with Racer Brown, cam grinder extraordinaire. The rocker tip is designed to "roll" over the valve tip in much the same way as the cam lobe is designed to "roll" across the bottom of a flat tappet while the tappet rotates.