Roller means that the tip of the rocker that contacts the valve stem is a metal wheel that rides on needle bearings. It helps reduce frictional losses. Non-roller rockers are just a solid piece of metal.
1.6 and 1.7 refer to the rocker's ratio. For example, with a 1.7 rocker, for every 1mm the pushrod moves the one end of the rocker upward, the other end pushes the valve 1.7mm downward. By increasing the rocker ratio you can cause the valves to open wider.
One concern with high-ratio rockers is that they can wear out your valve guides quicker because of increased side-loading on the valve stem. Roller tips can help redice side-loading somewhat.
I hope my explanation made some sense to you. If not please forgive me, I'm half drunk as I write this. :tongue