Basically getting some good advice here.
You (and anyone with our parts) are more than welcome to email me directly for advice/tuning/setup/etc of our parts. Sometimes I can respond right away, sometimes it takes a day or 2. I rarely have time to visit the boards much these days, so today is your lucky day!
This part you can do on the rack or ramps or whatever, doesn't matter. Do the install per assembly guide provided. Then shorten the driver side link all the way or real close to it, lock it down. Put the pass link close to same length to start out, and leave nuts loose & a few turns away from hex links. Then.....
Getting it onto dead level ground is VERY important. Next most important is even pressures in the rear tires. Fronts should be same also (side to side) but don't have to be same as rears. If still running airbags for further tuning ability, set them equally and as low as possible for your necessary ground clearance etc. You should be able to reach around the tire to get the feel of the pass link for neutral. You will feel it push the rod ends apart going one way, and pulling them together the other way (about a 2 turn area). Put it in the middle of that "neutral" area to start out & snug a nut or 2 by hand.
Then you can put it back on ramps or lift or even jack up on the bar to get more clearance to tighten up with wrenches. Be safe & use jack stands of course. The bar works fine to jack it up by, just protect that beautiful black powdercoat
As for preload, for MOST people neutral works just fine IF SET RIGHT. If in doubt how level the ground was etc, go by how the car "pushes" off the line or any change in tracking down the highway. You can adjust it a turn either way without getting into too much trouble, just mark it so you know where you started from, and always adj the pass side.
On faster cars, and more of the race-only guys, you can add preload for more violent launches. This is somewhat modifying our instructions, but even in the 10's, a little preload might help. If you are going straight & it drives straight, leave it as close to neutral as possible. If it still leans a little off the line & you have to drive it a little, then trying some preload might help. Basically, a mid 10 car could benefit from 1 turn, a mid 9 more like 2 turns, and mid 8's to mid 7's get 2-1/2 to 3 at most. A little goes a long way, it's VERY strong and tight. If you street drive it a lot, stay on the conservative side close to neutral.
As for driver in the car or not, seems to be not more than a half turn or so different for most. If it's convenient & you race it often, go for it. If you daily drive it a lot & not convenient, don't worry about it. Kinda splitting hairs there. Don't have to think "Oh no, what if a pass rides with me, do I need to reset it?", it's not that big of a deal.
Just remember, if ANYTHING CHANGES, always adj the bar LAST. Some people have added air to pass airbag with our bar, trying to improve things or maybe trying to correct an incorrect initial setting on the bar. If you don't reset the bar last, the bag is lifting the car & the bar is pulling it down, fighting against each other. When that happens, it will never work right or the same twice. I would say 98% set it as they should & it's perfect & doesn't need messed with again. The harder you launch or the less level your work area is, the more you might have to tweak it to get that sweet spot.
Shock settings & frame flex & bushing/control arm flex/etc/etc play into it all at faster levels. One 9 sec cars setting isn't perfect for another 9 sec car. If you got it set right, it should drive where you aim it, come out straight & hard, and corner like mad.