If you want to go the easy way, and not search junkyards, and mabye spend a few more bucks, go with the gto 5 lug front hubs from jspec.com, or tougefactory.com...even sometimes on ebay. they usually go from between $350-500 shipped depending on availablitly, but they're direct replacements for the stock front hubs...oh yeah, and 300zx brakes bolt right up once you have the hub in place, all you need is the 300zx lines, you can get braided lines front and rear for around $130.
IF you're going to do the 5 lugs for the rear, all you need is 300zx non turbo rear hubs, or s14 se rear hubs...they bolt right up to the stock upright, and then you can redrill the rear discs, or get s14 se discs, they bolt right up as well to the s13 caliper.
I've heard that doing the rear 300zx twin piston setup is overkill, with 300zx front brakes, 300zx master cylinder, and stock rear discs and good pads all around, the braking is very balanced, and the fronts will always lock up just before the rear does with (which is what you want)...
And if you really want to have fun once you have the 5-lug setup taken care of, throw some 12.5" vr-4 2 piece rotors on the front, with these adaptors
http://ztuner.com/brakes.php and 300zx tt calipers, you'll have a better than gt-r setup.