Using the above picture, look at the spacing between the roller bearings on the top rocker. Now look at the spacing between the roller bearings on this attached picture. I have read that when going to a roller rocker, the more bearing count the better for the load.
I have also read that when purchasing a roller bearing rocker, you need to purchase the shaft that is compatible with that bearing. As mentioned previously, the tolerances on the shaft must be held tighter on a roller bearing rocker.

I have seen "new" roller rockers for sale without shafts. They say to use existing shafts or can be used on stock shafts. This would scare me away from purchasing that rocker set. If I was to purchase a roller rocker set, I would want the shafts included.

Good thread!!