Looking at that first picture, it doesn't look very safe, we aren't saying anything in regards to that other than be careful. We would hate to have your wife post a note saying you had been hurt or dead. I am telling you, I know TWO people, we are talking two people I had sat down at a meal with who died under cars, it is no joke.
Do your measurements to the car it's self, do not go off the floor! Measure within the car, it's that simple. The measurements you are getting that are all different are likely because of what you are measuring from, the floor.
Let's look at how that floor was done.........
Yeah, that's a perfect thing to measure something I want within an 1/8" like a suspension mount on my hot rod.
Get the car level at those torque boxes then measure off the car.