Exhaust ports are the same between bigport and smallport, so all 16V 4AGE exhaust manifolds are interchangable (20V has the same ports and most bolts, but just the outer two bolts are positioned slightly differently).

Also if you already have a 4AGE running then changing to ZE isn't that bad. Yes you need loom and ECU and intercooler work, but the fuel system is already in place and so on. I'd guess the above prices are based on 4AC - 4AGZE.