Turns out I did not have the tools to drill precisely on center either. I could really feel the eccentricity on decent on single sheave I made so I had a friend who is a machinist make a flat faced sheave bushing. Now I have finally had a chance to alternate between the bearings and the single sheave on several climbs and will agree that the single sheave is better at reducing rope shift. Now I am curious why @SoftBankHawks has switch to using Petzl Vector from Sirius 500. It appears that Vector can not be spliced by hand. A disadvantage. What advantages does Vector offer?