shane, i was told by just about everyone i've asked about the nissan calipers, and they have said that they are a bad design and seize constantly. thats with normal road use with no mud and water and durt.
but come to think of it, it is only the older model nissans, such as the pintara, R30 and R31 skylines, and bluebirds, if you could find them.
i found a very good caliper, and just about perfect, its off a KF ford laser TX3. also, a newer proton sedan has a very similar rear caliper, so may look into those.
although, i may be wrong, as you've been looking into this for some time now.
cheers
Steve