I have mounted few scopes, but from what I have done if everything is straight and true it is a breeze. If something with the gun is off its a cluster duck. My savage something was off from the factory and burris sig. Z rings were a life saver.
I used a level on the cap at the time, but think it is a little off. Will try your trick and use the plumb line. I also had trouble with scope moving while torqueing it down, took 3 trys to get it right.
It's hell eatin em live