Backspace is the measurement from where the wheel mounts to the outer edge of the wheel on the mounting side should be around 5.79 inches on a 20x9 +20 offset
If it spins put jack under the lower control arm put some pressure up and use a pry bar to keep pressure down on the ball joint it shouldnt spin once its tight enough but if you are putting in lower spacers like that video you should be able to put them in with just taking the sway bar loose leaving upper ball joint alone and prying up on the shock bottom to slide spacer in good luck!
Edit: the allen key is just holding the ball joint from spinning also you would torque just the nut he is tightening with the adjustable when your done but it's not likely you will be able to get torque wrench in there so just tighten very tight when done
I had a coworker install my 2.5 Rough Country kit today. I can not figure out if he installed the top spacer. I am measuring ~38.5 in the front and ~39.75 in the rear. I have also attached a picture of the threads of one of the top bolts. Does it look like the top spacer is on there?
It's on there can't really see it but there would be threads showing on the studs like stated before!
I've been trying to decide between lifts also, looking at the Zone 4.5. I talked to someone from zone offroad the other day and he told me all the parts are the same for the 4.5 and 6.5 except the upper strut spacers in the front and the rear lift block which he said they will sell me if I decided 4.5 wasn't enough just throwing that out there.
The body lift won't change the ride I have the 1.5 zone and 2.5rc. The 2.5 made a slight difference and the E rated larger tires makes it a little more rough