U should have the car with appropriate weight in the front. Have the car sitting on the front wheels and block the back to level the rockers. You are going to have to put your 2x3 cross member in between the inner rockers inside the unibody at the appropriate distance from the rear axle. you should plate the unibody around that area. Now, depending on your tire height you will know your axle centerline from the floor, divide half the total tire height. Place ladder bar brackets on the housing and on the front crossmember. If the car has a low ride height and has a tall tire the bars will point downward a few degrees. Now that in a perfect world you have the car sitting level or how you like, install the shock brackets as per the spec for you shock distance.