Slant Six distributor question

The bottom slotted adjustment is set as to wear you want the vacuum advance to set, or if it gets in the way you can move the bottom slotted one to keep the vacuum advance from hitting the block or inner fender.. or so you can set the trimming farther one way or the other

I hope this makes seance, I would start in the middle and tighten it down, see if you can set the timing with it there with out the vacuum advance hitting anything