I can't answer your question but I would also like to learn the answer. It is obvious that if the spacers were placed under the frame, the truck's ride height would be relatively higher. None of the conversions I have seen online do that. Maybe if that is done the trailing arms miss the frame?
You build mounts for the rear of the lower control arms that drop down lower. There is a guy who blocked his under the chassis but I do not view that truck as safe so I am not going to give any links. The basic process is to add material under the rail & flip the upper shock tower support over.
You could box the rear mounts down 5/8 of an inch farther and put the 5/8 frame spacers between the bottom of the frame and the cv front end and easily get 5/8" I would think. Not sure if that's enough but its some and its easy. I had to make a boxed mount on the bottom of the frame for the rear mounts anyway so the height difference there doesn't really require any more work even.