Major fab work. New rims. Redrilled rotors(ewwww). And way out of wack brake bias/balance. Guess if you want to be innovative. The willwood calps fit, wonder how they compare size wise to the 3xtt calps and mounting position. Main question is the torque member and how it lines up or if something totaly custom would have to be made.
I tried doing the 300zx Brake upgrade on my B15 SE. The calipers bolted right up, but there are major clearance issues. Even with my aftermarket 40mm offset wheels, I STILL needed more clearance. This would mean wheel spacers, and possibly longer Nismo studs.
You also need to resize, and redril the 300zx rotors, not to mention getting custom brake lines. What looked to be a "budget" brake upgrade, soon turned into a 1,000 dollar nightmare.
I know SMC was looking into making a "kit", but I don't know what the current status of that is.
SMC makes their own big brake kit, it's been available for years. I have it on my SE-R. It has nothing to do with the 300ZX brakes though. The kit comes with a set of Wilwood lightweight 4 piston calipers, 11.75" slotted rotors, stainless steel brake lines, a custom made adapter to attach the caliper to the strut, and all the little bits and pieces you'll need to attach it. Mine even came with pads and brake fluid, it's an extremely complete kit, and it's really, really good.
Those are 16" wheels, which you will also need in order to clear the calipers. The Volk TE-37 wheel in 15" barely clears this brake kit, but I haven't found any other 15" wheel that does.