OME BP-51 lift height adjustment/coil springs confusion

I’m looking at the OME- BP-51 and would like to pull the trigger. But I’m super confused about the height adjustment. I want about 3” of lift to maintain the current height of my truck. The goal is to replace the spacer lift. I already have the RXT leaf pack on #2. In planning on adding a winch and a tube bumper plus rock sliders, roof rack and a decked drawer system. I travel with my wife, son and two dogs. So the truck is already heavy as is with all of us. I want a capable suspension that can handle extra weight for overlanding and allows me to do rock crawling when I’m out on my own. I cannot find the spring rate for the coil springs that come with the BP-51 nor can I find out how the lift height is adjusted. It seems to be down via pre load which I don’t want. Does anyone here have any insight?