Daniel;
On a 4x4 truck there is a short drag link from the steering box to the left front wheel. It pushed forward and backward on the steering arm to steer the truck. On a stock truck on flat ground this works OK, but add larger tires, taller springs, then go offroad, this short link can easily bind up when the suspension is flexed. Theres been times I've had to turn the steering all the way one direction to keep going straight, as the drag link is too short and as the axle droops, it starts to steer the front tires.
On crossover you put the steering box on like a 2wd, and then you make a crossover steering draglink that actually hooks to the right steering knuckle. Like what Ford has been doing since the 70's and how the newer dodges are. Now when the front end flexes, the longer draglink has a better arc and doesn't change the steering as badly. For some reason the trucks I've put crossover on tend to steer easier also, I think the leverage is better.
Now, in my experiance, a stock truck does not have enough clearance for crossover steering. My 75 dodge with a 4" lift would hit the pitman arm on the springs, and the draglink would hit the crossmember when flexed. When I put it on my 90, I put a drop in the draglink and it has a 6" lift and it seems to work well, without hitting anything. Like above I suggest you get your parts for the lift and the steering and do it all at once. I do have pics of the crossover on my 75 in the readers rigs.
Michael