Do you know if it matters if the engine and manifolds come from the same make/model? I am fairly confident I can make some factory manifolds work, but not the Escalade's manifolds. I also have no hope of utilizing the factory GM cats in their stock position. I can probably get them close, but they would be new aftermarket cats.
For the manifolds you want to stick to factory cast parts, because they look stock. You want to stay away from any kind of tube manifolds/headers. Those would be an instant fail on the visual, unless they have a CARB#. It would be best to retain the factory cat, re-routing the pipes to relocate them is sketchy just because these smog guys are afraid of losing their license's. Some of them will fail you if they are unsure of how to proceed. They get "undercover" cars sometimes trying to catch them doing illegal smogs.