Personally, I have only done one of these so I don't have a lot to offer. One of the mistakes people make is thinking that mating it up to the truck frame and how and where it's welded is the most important thing, when really that is the least important. The most important is getting the suspension on that sub frame in proper relation to the truck frame! So getting the frame and the sub frame at ride height, and knowing the wheel base is right and the geometry on the sub is correct is MOST important.
But I ran an "all thread" to replace the shocks on the clip. I then tightened them up to drop frame down until the lower control arms were level, and the distance between the arm and the rubber bumper was the same as when it was on the Camaro. Being the Camaro and the truck are pretty close in weight, this worked out well.
The trucks frame was dropped down to the height I wanted it too, the rear could be done first to be sure.
This way all you have to worry about is getting the wheel base right, everything else is going to happen as needed.
One important thing is check the upper control arm shaft angle with an angle finder while it's on the Camaro so you know what to put it at on the truck.
Tack the frame into place and then install the front sheet metal on the truck to be sure the wheels look perfectly centered in the wheel wells. Then go back and finish welding it in place.
If you do all this, the front will suspension will align exactly as it did on the Camaro. You can tell the alignment shop to ignore what they are looking at and align a Camaro.
Brian