You are most likely referring to Gold Crown I's. The Gold Crown II was only made from 1975-1977 and is pretty rare. Many people think they have a GCII because of features like adjustable feet, floating nut plates in the rails, metal nameplate, etc., but all of those were implemented in the GCI production by 1964. The GCII was merely an aesthetic change featuring rosewood stained aprons and pedestal with bronze feet and ball tray bezel.
How did you get the Gold Crown IV pocket castings to fit on a Gold Crown I? The rails on the GCIV are wider. Did you just swap the whole top out (castings, rails, aprons)?