You are right - I was 99.9% wrong The bayonet and pressure rating (0.9) is the same, but the seating depth of the JZX81/1JZ item is shallower.
I checked the other Toyotas (Hilux, Corolla, Lexus/Camry) here, and they are all the same depth as the Cressida (or totally different for the Hilux).
The weird thing is my EPG lists the same part number (16401-72090) for both 7MGE and 1JZ# (and MX83 / JZX81). But that is the Japan EPG, so maybe their 7MGEs had the same radiator as the 1JZ.
I guess your best bet is to take that part number to Repco or wherever and see what they can do. Or clean up your garage and find your original cap