damn good question. curious to know myself. I would think you would need the entire system for it to fit properly. You cant just add Z33 brembo calipers to Z33 that didn't come with brembos....so I would assume you couldn't either. Problem is (with the Z33), you need the calipers, rotors, lines, etc to swap them on a non-brembo Z33.
If all you have is the calipers, then i would say sell them on ebay and just do a stage 2 brake upgrade. Reason being is the remaining things you need to buy (if they fit) are not very cheap. I see alot of Z33 guys selling their brembos for a pretty penny....plus its USED. Stoptech offers a stage 2 brake kit for $600-700. comes with slotted or crossdrilled rotors, axxis or hawks pads, steel braided lines, and race brake fluid. This might be a better choice in the long run. and you'd be getting NEW parts. I'll dig around and see if I cant find an answer to your question though.