Backhalfing my truck and need a little help.

[team39763]

I got the new frame assembly set in between the stock frame rails. Now I'm just trying to square and level things up as best I can. What is the maximum allowable tolerance/difference? My main crossmember measures 6 23/32 to 6 25/32 on one side and the other measures 6 25/32 to 6 3/4. I guess it just depends who's measuring and how they hold the tool. I used both a laser measuring tool and a tape measurer. I'm about to go buy some plumb bobs to get my centerline mapped on the floor, I'm sure that'll help too.
Also, do I need to account for from suspension ride height? Most directions say to just get the chassis up in the air and level. I was wondering if I put my backhalf in a level height, would it change my ladder bar angle when I drop it down to ride height?