The 20v CAS won't go into a 16v... you NEED the one off the GZE if you're going to keep coilpack ignition.
Also the injectors are different. Can't use 20v ones in the 16v.

Other than that it should all be pretty straight forward depending on the 20v water system was setup.
But there will no doubt be changes required in the ECU, doubt it'll run with exactly the same settings.