Another way to center the reticle is to place the ocular end against a mirror and then while looking through the objective end adjust the turrets until the actual reticle and mirror image of it line up so that only one reticle is visible.

Personally, I've never liked those Leupold std. mounts. The dual dovetails would be my preference. Then again, I don't currently use Leupold mounts on any of my rifles, preferring Talleys instead.